Electron beam apparatus and method of manufacturing semiconductor device using the apparatus

ABSTRACT

The present invention provides an electron beam apparatus for irradiating a sample with primary electron beams to detect secondary electron beams generated from a surface of the sample by the irradiation for evaluating the sample surface. In the electron beam apparatus, an electron gun has a cathode for emitting primary electron beams. The cathode includes a plurality of emitters for emitting primary electron beams, arranged apart from one another on a circle centered at an optical axis of a primary electro-optical system. The plurality of emitters are arranged such that when the plurality of emitters are projected onto a straight line parallel with a direction in which the primary electron beams are scanned, resulting points on the straight line are spaced at equal intervals.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a technique for testing orinspecting a property or aspect of a sample such as a wafer. In moredetail, the present invention relates to an electron beam apparatusapplicable to a defect detection and/or line width measurement of awafer during a semiconductor manufacturing process and so on, in whichelectron beams are irradiated to a sample, secondary electrons emittedfrom the sample and varying according to a property of the samplesurface are captured, and image data is created therefrom to evaluatepatterns on the sample surface with a high throughput on the basis ofthe image data. The present invention also relates to an evaluationsystem and a semiconductor device manufacturing method, both of whichutilize the electron beam apparatus. In the present description, themeaning of the term “evaluation” of a sample also includes the meaningof “inspections” such as defect detection and line width measurement ofa sample.

[0002] In semiconductor processes, design rules are now going to enterthe era of 100 nm, and the production scheme is shifting from small-kindmass production represented by DRAM to a multi-kind small productionsuch as SOC (silicon on chip). Associated with this shifting, the numberof manufacturing steps has been increased, and an improved yield of eachprocess is essential, so that testing for defects caused by the processbecomes important.

[0003] With the trend of increasingly higher integration ofsemiconductor devices and finer patterns, a need exists for highresolution, high throughput testing apparatuses. A resolution of 100 nmor less is required for examining defects on a wafer of 100 nm designrule. Also, as manufacturing steps are increased in response to therequirement of higher integration of devices, the amount of testing isincreased and thus a higher throughput is required. Further, as devicesare formed of an increased number of layers, testing apparatuses arerequired to have the ability to detect defective contacts (electricdefect) of vias which connect lines on layers to each other. Whileoptical defect testing apparatuses are mainly used at present, it isanticipated that electron beam based defect testing apparatuses willsubstitute for optical defect testing apparatus as a dominant testingapparatus in the future from a viewpoint of the resolution and defectivecontact testing capabilities. However, the electron beam based defecttesting apparatus also has a disadvantage in that it is inferior to theoptical one in the throughput. For this reason, a need exists for thedevelopment of a high resolution, high throughput electron beam basedtesting apparatus which is capable of electrically detecting defects.

[0004] It is said that the resolution of an optical defect testingapparatus is limited to one half of the wavelength of used light, andthe limit is approximately 0.2 μm in an example of practically usedoptical defect detecting apparatus which uses visible light. On theother hand, in electron beam based systems, scanning electronmicroscopes (SEM) have been commercially available. The scanningelectron microscope has a resolution of 0.1 μm and takes a testing timeof eight hours per 20 cm wafer. The electron beam based system also hasa significant feature that it is capable of testing electric defects(broken lines, defective conduction of lines, defective conduction ofvias, and so on). However, it takes so long testing time that it isexpected to develop a defect testing apparatus which can rapidly conducta test. Further, a testing apparatus is expensive and low in throughputas compared with other process apparatuses, so that it is presently usedafter critical steps, such as after etching, deposition (includingcopper coating), CMP (chemical-mechanical polishing) planarizationprocessing, and so on.

[0005] A testing apparatus in accordance with an electron beam basedscanning (SEM) scheme will be described. An SEM based testing apparatusnarrows down an electron beam which is linearly irradiated to a samplefor scanning. The diameter of the electron beam corresponds to theresolution. On the other hand, by moving a stage in a directionperpendicular to a direction in which the electron beam is scanned, aregion under observation is tow-dimensionally irradiated with theelectron beam. In general, the width over which the electron beam isscanned, extends over several hundred μm. Secondary electron beamsemitted from the sample by the irradiation of the focussed electron beam(called the “primary electron beam”) are detected by a combination of ascintillator and a photomultiplier (photomultiplier tube) or asemiconductor based detector (using PIN diodes). The coordinates ofirradiated positions and the amount of the secondary electron beams(signal strength) are combined to generate an image which is stored in astorage device or output on a CRT (Braun tube). The foregoing is theprinciple of SEM (scanning electron microscope). From an image generatedby this system, defects on a semiconductor (generally, Si) wafer isdetected in the middle of a manufacturing procedure. A detecting speedcorresponding to the throughput, is determined by the intensity of aprimary electron beam (current value), a size of a pixel, and a responsespeed of a detector. Currently available maximum values are 0.1 μm forthe beam diameter (which may be regarded as the same as the resolution),100 nA for the current value of the primary electron beam, and 100 MHzfor the response speed of the detector, in which case it is said that atesting speed is approximately eight hours per wafer of 20 cm diameter.Therefore, there exists a problem that a testing speed is significantlylow in comparison with that in an optical based testing apparatus. Forinstance, the former testing speed is {fraction (1/20)} or less of thelatter testing speed.

[0006] If a beam current is increased in order to achieve a highthroughput, a satisfactory SEM image cannot be obtained in the case of awafer having an insulating membrane on its surface because chargingoccurs.

[0007] As another method for improving an inspection speed, in terms ofwhich an SEM system is poor, there have been proposed SEM systems(multi-beam SEM systems) and apparatuses employing a plurality ofelectron beams. According to the systems and apparatuses, an inspectionspeed is improved in proportion to the number of electron beams.However, as a plurality of primary electron beams impinge obliquely on awafer and a plurality of secondary electron beams are pulled from thewafer obliquely, only secondary electrons released obliquely from thewafer are caught by a detector. Further, a shadow occasionally appearson an image and secondary electrons from a plurality of electron beamsare difficult to separate from one another, which disadvantageouslyresults in a mix of the secondary electrons.

[0008] Still further, there has been no suggestion or considerationabout an interaction between an electron beam apparatus and othersub-systems in an evaluation system employing a multi-beam basedelectron beam apparatus and thus, at present there aren't any completeevaluation systems of a high throughput. In the meantime, as a wafer tobe inspected becomes greater, sub-systems must be re-designed toaccommodate to a greater wafer, a solution for which has not yet beensuggested either.

SUMMARY OF THE INVENTION

[0009] The present invention has been accomplished with a view toobviating the aforementioned problems of prior art and therefore, it isan object of the present invention to provide an evaluation systememploying an SEM electron beam apparatus of a multi-beam type andespecially an evaluation system capable of improving a throughput ofinspection processing.

[0010] It is another object of the present invention to provide an SEMelectron beam apparatus of a multi-beam type capable of improving notonly a throughput of inspection processing but also detection accuracy.

[0011] It is still another object of the present invention to provide amethod of manufacturing semiconductor devices, according to which asemiconductor wafer can be evaluated by utilizing such an electron beamapparatus or evaluation system as mentioned above irrespective ofwhether it is in the middle of a fabrication process or upon completionof a fabrication process.

[0012] In order to achieve the above objects, the present invention isconstituted as follows. That is, a plurality of primary electron beams(multi-beam) are employed to scan a sample in the one-dimensionaldirection (X direction). The primary electron beams pass through an ExBfilter (Wien filter) to impinge perpendicularly upon the surface of thesample, and secondary electrons released from the sample are separatedfrom the primary electron beams by the ExB filter to be pulled obliquelyin relation to the axis of the primary electron beams to converge orform an image on a detection system by means of a lens system. Then, astage is moved in the perpendicular direction (Y direction) with respectto the primary electron beam scanning direction (X direction) to obtaincontinuous images.

[0013] When the primary electron beams pass through the ExB filter, acondition (Wien condition) where the force applied to the electron beamsfrom the electrical field is equal to the force applied from themagnetic field and the directions of the forces are opposite, is set sothat the primary electron beams go straight. On the other hand, sincethe secondary electrons and the primary electron beams advance in theopposite directions, the directions of the forces applied to thesecondary electrons from the electrical field and magnetic field are thesame and thus, the secondary electrons are deflected from the axialdirection of the primary electron beams. As a result, the primaryelectron beams and secondary electron beams are separated from eachother. When electron beams pass through an ExB filter, aberration islarger if the electron beams curve than if the electron beams travelstraight. Given that, the optical system of the present invention isdesigned in such a manner as to cause primary electron beams, whichrequire low aberration, to go straight and cause secondary electronbeams, which do not necessarily require low aberration, to deflect.

[0014] A detection system of the present invention consists of detectorsrespectively corresponding to primary electron beams, which are arrangedsuch that a secondary electron deriving from its corresponding primaryelectron beam impinges on the corresponding detector by means of animage-formation system, whereby interaction of signals, that is,cross-talk can be substantially reduced. As a detector, a combination ofa scintillator and a photomultiplier, a PIN diode, etc. may be employed.In the electron beam apparatus according to one embodiment of thepresent invention, sixteen primary electron beams are employed and abeam current of 20 nA having a beam diameter of 0.1 Mm is obtained fromeach of them and therefore, a value of current obtained from the sixteenelectron beams in the electron beam apparatus is three times as great asthat obtained from the commercially available apparatus at present.

[0015] Further, an electron gun for the electron beam apparatus of thepresent invention uses a thermal cathode as an electron beam source, andLaB6 is employed as an electron emitting material (emitter). Othermaterials may be used as long as they have a high melting point (lowsteam pressure at high temperatures) and small work function. In thepresent invention, two different ways of providing multiple electronbeams are employed. One is to pull one electron beam from an emitter(with one protrusion) and pass the electron beam through a thin platewith a plurality of apertures, thereby obtaining a plurality of electronbeams. The other is to provide an emitter with a plurality ofprotrusions and pull a plurality of electron beams directly from theprotrusions. The both ways make use of the properties of an electronbeam that an electron beam is more easily emitted from the tip of aprotrusion. Electron beams from an electron beam source employing othermethods, for example, thermal field emission type electron beams may beemployed. A thermal electron beam source uses a system for heating anelectron emission material to emit electrons, whereas a thermal fieldemission electron beam source uses a system for applying a high electricfield to an electron emission material to emit electrons and furtherheating an electron beam emission portion to stabilize electronemission.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is an elevation view illustrating major components of anevaluation system according to the present invention.

[0017]FIG. 2 is a plan view illustrating major components of theevaluation system indicated in FIG. 1 seen from above along the line inB-B in FIG. 1;

[0018]FIG. 3 illustrates a relationship between a wafer transfer chamberand a loader;

[0019]FIG. 4 is a cross section of the mini environment device shown inFIG. 1 taken along the line C-C in FIG. 1;

[0020]FIG. 5 illustrates the loader housing indicated in FIG. 1 seenalong the line D-D in FIG. 2;

[0021]FIG. 6 is an enlarged view of the wafer rack, in which FIG. 6A isa side view thereof and FIG. 6B is a cross section thereof taken alongthe line E-E in FIG. 6A;

[0022]FIG. 7 illustrates a variation of a method of supporting a mainhousing;

[0023]FIG. 8 schematically illustrates an embodiment of an electron beamapparatus concerning the present invention, which can be applied to theevaluation system indicated in FIG. 1;

[0024]FIG. 9A illustrates an arrangement of apertures bored on amulti-aperture plate used in primary and secondary optical systems ofthe electron beam apparatus shown in FIG. 8, and FIG. 9B depicts a modeof primary electron beam scanning;

[0025]FIGS. 10A and 10B illustrate embodiments of an ExB separatorapplicable to the electron beam apparatus concerning the presentinvention;

[0026]FIG. 11 illustrates a potential application system applicable tothe electron beam apparatus concerning the present invention;

[0027]FIG. 12 illustrates an electron beam calibration mechanismapplicable to the electron beam apparatus concerning the presentinvention, in which FIG. 12A is a side view thereof and FIG. 12B is aplan view thereof;

[0028]FIG. 13 schematically illustrates a device for controlling analignment of wafers, which is applicable to the electron beam apparatusconcerning the present invention;

[0029]FIG. 14 illustrates a relationship between an X-Y stage and acharged particle beam irradiation means of an electron optical system ina conventional electron beam apparatus;

[0030]FIG. 15 illustrates the state of the bottom of the X-Y stageindicated in FIG. 14;

[0031]FIG. 16 illustrates a relationship between an X-Y stage and acharged particle beam irradiation means of an electron optical systemaccording to an embodiment of an electron beam apparatus of the presentinvention;

[0032]FIG. 17 illustrates a relationship between an X-Y stage and acharged particle beam irradiation means of an electron optical systemaccording to another embodiment of an electron beam apparatus of thepresent invention;

[0033]FIG. 18 illustrates a relationship between an X-Y stage and acharged particle beam irradiation means of an electron optical systemaccording to still another embodiment of an electron beam apparatus ofthe present invention;

[0034]FIG. 19 illustrates a relationship between an X-Y stage and acharged particle beam irradiation means of an electron optical systemaccording to further another embodiment of an electron beam apparatus ofthe present invention;

[0035]FIG. 20 illustrates a relationship between an X-Y stage and acharged particle beam irradiation means of an electron optical systemaccording to still another embodiment of an electron beam apparatus ofthe present invention;

[0036]FIG. 21 illustrates a relationship between an X-Y stage and acharged particle beam irradiation means of an electron optical systemaccording to still another embodiment of an electron beam apparatus ofthe present invention;

[0037]FIG. 22 illustrates an operation emission mechanism installed inthe embodiment indicated in FIG. 21;

[0038]FIG. 23 illustrates a gas circulation piping mechanism installedin the embodiment indicated in FIG. 21;

[0039]FIG. 24 schematically illustrates an embodiment of an electronoptical system contained in an electron beam apparatus of the presentinvention;

[0040]FIG. 25 illustrates an example of an arrangement of emitter chipsconstituting an electron gun employed in an electron optical system ofan electron beam apparatus of the present invention;

[0041]FIG. 26 illustrates another example of an arrangement of emitterchips constituting an electron gun employed in an electron opticalsystem of an electron beam apparatus of the present invention;

[0042]FIG. 27 illustrates still another example of an arrangement ofemitter chips constituting an electron gun employed in an electronoptical system of an electron beam apparatus of the present invention;

[0043]FIG. 28 schematically illustrates another embodiment of anelectron optical system contained in an electron beam apparatus of thepresent invention;

[0044]FIG. 29 is a plan view of a cathode tip portion (emitter) of anelectron gun applicable to an electron optical system contained in anelectron beam apparatus of the present invention;

[0045]FIG. 30 is a side view of the cathode shown in FIG. 29;

[0046]FIG. 31 is a plan view of a cathode tip portion of an electron gunapplicable to an electron optical system installed in an electron beamapparatus of the present invention;

[0047]FIG. 32 is a side view illustrating a relationship between anemitter of the cathode shown in FIG. 31 and a Wehnelt;

[0048]FIG. 33 is a cross section illustrating an alignment mechanism foraligning an emitter of a cathode with an opening of a Wehnelt;

[0049]FIG. 34A is a plan view of a cathode tip portion of an electrongun applicable to an electron optical system contained in an electronbeam apparatus concerning the present invention, and FIG. 34B is a sideview of emitters thereof;

[0050]FIG. 35 is a side view of the cathode shown in FIG. 34;

[0051]FIGS. 36A and 36B are plan and side views of a machine tool formachining an emitter of the cathode shown in FIGS. 34 and 35;

[0052]FIG. 37 is a plan view of a Wehnelt constituting, together withthe cathode shown in FIG. 34, an electron gun;

[0053]FIG. 38 is a cross sectional view showing the state where thecathode shown in FIG. 34 and the Wehnelt shown in FIG. 37 are combined;

[0054]FIG. 39A is a plan view of a cathode tip portion of an electrongun applicable to an electron optical system contained in an electronbeam apparatus concerning the present invention, and FIGS. 39B and 39Care side views of emitters thereof;

[0055]FIG. 40 is an illustration showing that when emitters consistingof the plurality of protrusions shown in FIG. 41 are projected on theX-axis, the protrusions show up at equal spaces;

[0056]FIG. 41 is a side view of an electron gun in which the cathodeshown in FIG. 39 is incorporated;

[0057]FIG. 42A is a plan view of a cathode tip portion of an electrongun applicable to an electron optical system contained in an electronbeam apparatus of the present invention, and FIG. 42B is a side view ofemitters thereof;

[0058]FIG. 43 schematically illustrates another embodiment of anelectron beam apparatus of the present invention;

[0059]FIG. 44 is a cross section of multi-beam emitted from an electrongun of an electron optical system contained in the electron beamapparatus shown in FIG. 43 on the X-Y plane perpendicular to the opticalaxis;

[0060]FIG. 45 is an illustration explaining a principle according towhich information about a location deeper than the surface of a samplesuch as a wafer, etc. is obtained;

[0061]FIG. 46 is a graph representing a relationship between primaryelectron energy and secondary electron energy generated by the primaryelectron energy;

[0062]FIG. 47 schematically illustrates another embodiment of anelectron beam apparatus of the present invention;

[0063]FIG. 48 schematically illustrates still another embodiment of anelectron beam apparatus of the present invention;

[0064]FIG. 49 shows a layout of standard marks mounted on an X-Y stageof the electron beam apparatus shown in FIG. 48;

[0065]FIG. 50 shows waveforms representing a signal contrast in the casethat electron beams of various beam diameters scan the standard marks bymeans of the electron beam apparatus shown in FIG. 48;

[0066]FIG. 51 schematically illustrates further another embodiment of anelectron beam apparatus of the present invention;

[0067]FIG. 52 is an illustration explaining measurement of an amount ofradiation by an electron beam apparatus of the present invention;

[0068]FIG. 53 schematically illustrates still another embodiment of anelectron beam apparatus of the present invention;

[0069]FIG. 54 is a plan view showing an arrangement of devices on asingle wafer;

[0070]FIG. 55 schematically illustrates still another embodiment of anelectron beam apparatus of the present invention;

[0071]FIG. 56 schematically illustrates further another embodiment of anelectron beam apparatus of the present invention;

[0072]FIG. 57 is a functional block diagram indicating a defectdetection means (evaluation means) of the electron beam apparatus shownin FIG. 56;

[0073]FIG. 58 is a flow chart that depicts the process of detectingdefects conducted in an electron beam apparatus concerning the presentinvention;

[0074]FIG. 59 is an illustration explaining defect detection by means ofcomparison between dies, measurement of a line width, measurement ofvoltage contrast in the defect detection process described in FIG. 58;

[0075]FIG. 60 schematically illustrates still another embodiment of anelectron beam apparatus concerning the present invention;

[0076]FIG. 61 is a flow chart depicting a main routine in the case ofwafer inspection conducted by means of the electron beam apparatus shownin FIG. 60;

[0077]FIG. 62 is a conceptual diagram of a plurality of regions to beinspected, which are staggered and partially overlapped on a wafer;

[0078]FIG. 63 illustrates a plurality of images to be inspected, whichare obtained by an electron beam apparatus concerning the presentinvention, and a referential image;

[0079]FIG. 64 is a flow chart that depicts the process of obtaining dataabout an image to be inspected, which is a sub-routine of the mainroutine indicated in FIG. 61;

[0080]FIG. 65 is a flow chart depicting a comparison process, which is asub-routine of the main routine indicated in FIG. 61;

[0081]FIG. 66 is a flow chart that depicts the process of inspection(evaluation) concerning the present invention;

[0082]FIG. 67 is a flow chart depicting a method of fabricating asemiconductor device concerning the present invention; and

[0083]FIG. 68 is a flow chart depicting the details of the lithographyprocess indicated in FIG. 67.

BEST MODE FOR IMPLEMENTING THE INVENTION

[0084] In the following, embodiments of a evaluation system according tothe present invention will be described in a case that evaluationsamples are semiconductor substrates or wafers having patterns onsurfaces thereof. It should be noted that samples other than the waferare applicable.

[0085]FIGS. 1 and 2 respectively shows a cross-sectional and plan viewsillustrating main components of evaluation system 1 according to anembodiment of the present invention. The evaluation system 1 comprises acassette holder 10 for holding a cassette which stores a plurality ofwafers; a mini-environment chamber 20; a main housing 30; a loaderhousing 40 disposed between the mini-environment chamber 20 and the mainhousing 30 to define two loading chambers; a loader 60 for loading awafer from the cassette holder 10 (onto a stage apparatus 50 disposed inthe main housing 30); the stage apparatus 50 for carrying and moving thewafer W; and an electro-optical system 70 installed in the vacuum mainhousing 30. These components are arranged in a positional relationshipas illustrated in FIGS. 1 and 2. The evaluation system further comprisesa pre-charge unit 81 disposed in the vacuum main housing 30; a potentialapplying mechanism 83 (see in FIG. 11) for applying a wafer with apotential; an electron beam calibration mechanism 85 (see in FIG. 12);and an optical microscope 871 which forms part of an alignmentcontroller 87 for aligning the wafer on the stage apparatus 50.

[0086] Constitutions of the main components (sub-system) will next beexplained in detail.

[0087] Cassette Holder 10

[0088] The cassette holder 10 is configured to hold a plurality (two inthis embodiment) of cassettes c (for example, closed cassettes such asSMIF, FOUP manufactured by Assist Co.) in which a plurality (forexample, twenty-five) wafers are placed side by side in parallel,oriented in the vertical direction. The cassette holder 10 can bearbitrarily selected for installation adapted to a particular loadingmechanism. Specifically, when a cassette is automatically loaded intothe cassette holder 10 by a robot or the like, the cassette holder 10having a structure adapted to the automatic loading can be installed.When a cassette is manually loaded into the cassette holder 10, thecassette holder 10 having an open cassette structure can be installed.In this embodiment, the cassette holder 10 is a type adapted to theautomatic cassette loading, and comprises, for example, an up/down table11, and an elevating mechanism 12 for moving the up/down table 11 up anddown. The cassette c can be automatically set onto the up/down table 11in a state indicated by chain lines in FIG. 2. After the setting, thecassette c is automatically rotated to a state indicated by solid linesin FIG. 2 so that it is directed to the axis of pivotal movement of afirst carrier unit within the mini-environment chamber 20. In addition,the up/down table 11 is moved down to a state indicated by chain linesin FIG. 1. In this way, since the cassette holder 10 for use inautomatic loading, or the cassette holder 10 for use in manual loadingmay be both implemented by those in known structures, detaileddescription on their structures and functions are omitted.

[0089]FIG. 3 shows a modification to a mechanism for automaticallyloading a cassette. A plurality of 300 mm wafers W are contained in aslotted pocket (not shown) fixed to the inner surface of a chamber 501for carriage and storage. This wafer carrying section 24 comprises achamber 501 of a squared cylinder, a wafer carrying in/out door 502connected to the chamber 501 and an automatic opening apparatus for adoor at a substrate carrying in/out aperture positioned at a side of thechamber 501 and capable of opening and closing mechanically theaperture, a cap 503 positioned in opposite to the aperture for coveringan aperture for the purpose of detachably mounting filers and fanmotors, and a slotted pocket 507 for holding a wafer W. In thisembodiment, the wafers are carried in and out by means of a robot typecarrying unit 612 of the loader 60.

[0090] It should be noted that wafers accommodated in the cassette c aresubjected to testing which is generally performed after a process forprocessing the wafers or in the middle of the process withinsemiconductor manufacturing processes. Specifically, accommodated in thecassette are wafers which have undergone a deposition process, CMP, ionimplantation and so on; wafers each formed with wiring patterns on thesurface thereof; or wafers which have not been formed with wiringpatterns. Since a large number of wafers accommodated in the cassette care spaced from each other in the vertical direction and arranged sideby side in parallel, and the first carrier unit has an arm which isvertically movable, a wafer at an arbitrary position can be held by thefirst carrier unit which will be described later in detail.

[0091] Mini-Environment Device 20

[0092] In FIG. 4 shows an elevation of the mini-environment device 20 ina direction different to that in FIG. 1. As illustrated in FIG. 4 aswell as FIGS. 1 and 2, the mini-environment device 20 comprises ahousing 22 defining a mini-environment space 21 that is controlled forthe atmosphere; a gas circulator 23 for circulating a gas such as cleanair within the mini-environment space 21 to execute the atmospherecontrol; a discharger 24 for recovering a portion of air supplied intothe mini-environment space 21 to discharge it; and a prealigner 25 forroughly aligning a sample, i.e., a wafer placed in the mini-environmentspace 21.

[0093] The housing 22 has a top wall 221, bottom wall 222, andperipheral wall 223 which surrounds four sides of the housing 22, toprovide a structure for isolating the mini-environment space 21 from theoutside. For controlling the atmosphere in the mini-environment space21, as illustrated in FIG. 4, the gas circulator 23 comprises a gassupply unit 231 attached to the top wall 221 within the mini-environmentspace 21 for cleaning a gas (air in this embodiment) and delivering thecleaned gas downward through one or more gas nozzles (not shown) inlaminar flow; a recovery duct 232 disposed on the bottom wall 222 withinthe mini-environment space for recovering air which has flown down tothe bottom; and a conduit 233 for connecting the recovery duct 232 tothe gas supply unit 231 for returning recovered air to the gas supplyunit 231.

[0094] In this embodiment, the gas supply unit 231 takes about 20% ofair to be supplied, from the outside of the housing 22 to clean the airin the mini-environment space 21. However, the percentage of gas takenfrom the outside may be arbitrarily selected. The gas supply unit 231comprises an HEPA or ULPA filter in a known structure for creatingcleaned air. The laminar down-flow of cleaned air is mainly suppliedsuch that the air passes a carrying surface formed by the first carrierunit (which is described later) disposed within the mini-environmentspace 21 to prevent particle particles, which could be produced by thecarrier unit, from attaching to the wafer. Therefore, the down-flownozzles need not be positioned near the top wall as illustrated, but isonly required to be above the carrying surface formed by the carrierunit. In addition, the air is not supplied over the entiremini-environment space 21. It should be noted that an ion wind may beused as cleaned air to ensure the cleanliness. Also, a sensor may beprovided within the mini-environment space 21 for observing thecleanliness such that the apparatus is shut down when the cleanliness isdegraded. An access port 225 is formed in a portion of the peripheralwall 223 of the housing 22 that is adjacent to the cassette holder 10. Agate valve in a known structure may be provided near the access port 225to shut the port from the mini-environment device 20. The laminardown-flow near the wafer may be, for example, at a rate of 0.3 to 0.4m/sec. The gas supply unit 231 may be disposed outside themini-environment space 21 instead of within the space.

[0095] The discharger 24 comprises a suction duct 241 disposed at aposition below the wafer carrying surface of the carrier unit and belowthe carrier unit; a blower 242 disposed outside the housing 22; and aconduit 243 for connecting the suction duct 241 to the blower 242. Thedischarger 24 aspires a gas flowing down around the carrier unit andincluding particle, which could be produced by the carrier unit, throughthe suction duct 241, and discharges the gas outside the housing 22through the conduits 243, 244 and the blower 242. In this event, the gasmay be discharged into an pumping pipe (not shown) which is laid to thevicinity of the housing 22.

[0096] The prealigner 25 disposed within the mini-environment space 21optically or mechanically detects an orientation flat (which refers to aflat portion formed along the outer periphery of a circular wafer andhereunder called as ori-fla) formed on the wafer, or one or moreV-shaped notches formed on the outer peripheral edge of the wafer, andpreviously aligns the position of the waver in a rotating directionabout the axis O₁-O₁ at an accuracy of approximately±one degree. Theprealigner forms part of a mechanism for determining the coordinates ofthe wafer, and executes a rough alignment of the wafer. Since theprealigner itself may be of a known structure, explanation on itsstructure and operation is omitted. Though not shown, a recovery ductfor the discharger may also be provided below the prealigner so that airincluding particle discharged from the prealigner, may be discharged tothe outside.

[0097] Main Housing 30

[0098] As illustrated in FIGS. 1 and 2, the main housing 30 whichdefines the working chamber 31, comprises a housing body 32 that issupported by a housing supporting device 33 carried on a vibrationisolator 37 disposed on a base frame 36. The housing supporting device33 comprises a frame structure 331 assembled into a rectangular form.The housing body 32 comprises a bottom wall 321 mounted on and securelycarried on the frame structure 331; a top wall 322; and a peripheralwall 323 which is connected to the bottom wall 321 and the top wall 322and surrounds four sides of the housing body 32, thereby isolating theworking chamber 31 from the outside. In this embodiment, the bottom wall321 is made of a relatively thick steel plate to prevent distortion dueto the weight of equipment carried thereon such as the stage apparatus50. Alternatively, another structure may be employed. In thisembodiment, each of the housing body 32 and the housing supportingdevice 33 is assembled into a rigid construction, and the vibrationisolator 37 blocks vibrations from the floor, on which the base frame 36is installed, from being transmitted to the rigid structure. A portionof the peripheral wall 323 of the housing body 32 that adjoins theloader housing 40 is formed with an access port 325 for introducing andremoving a wafer.

[0099] The vibration isolator may be either of an active type which hasan air spring, a magnetic bearing and so on, or a passive type likewisehaving these components. Since any known structure may be employed forthe vibration isolator, description on the structure and functions ofthe vibration isolator itself is omitted. The working chamber 31 is keptin a vacuum atmosphere by a vacuum system (not shown) in a knownstructure. A controller 2 for controlling the operation of the overallevacuation system is disposed below the base frame 36.

[0100] In the evaluation system 1, some housings including the mainhousing 30 are kept in vacuum atmosphere. A system for evaporating sucha housing comprises a vacuum pump, vacuum valve, vacuum gauge, andvacuum pipes, and evaporates the housing such as an electro-opticalsystem portion, detector portion, wafer housing, load lock housing orthe like, in accordance with a predetermined sequence. The vacuum valvesare adjusted to kept a required vacuum level of the housings. Further,the vacuum levels are always monitored, and when an abnormal vacuumlevel is detected, an interlock function enables isolation valves toshut dawn the path between chambers or between a chamber and a pumpingsystem to kept the required vacuum level of the housing. As to thevacuum pump, a turbo-molecular pump can be utilized for main evacuation,and a dry pump of a Roots type can be utilized for rough evacuation. Thepressure at a test location (electron beam irradiated region) is 10⁻³ to10⁻⁵ Pa. Preferably, pressure of 10⁻⁴ to 10⁻⁶ Pa is practical.

[0101] Loader Housing 40

[0102]FIG. 5 shows an elevation of the loader housing 40, in view of thedirection different to that in FIG. 1. As illustrated in FIG. 5 as wellas FIGS. 1 and 2, the loader housing 40 comprises a housing body 43which defines a first loading chamber 41 and a second loading chamber42. The housing body 43 comprises a bottom wall 431; a top wall 432; aperipheral wall 433 which surrounds four sides of the housing body 43;and a partition wall 434 for partitioning the first loading chamber 41and the second loading chamber 42 to isolate the two loading chambersfrom the outside. The partition wall 434 is formed with an aperture,i.e., an access port 435 for passing a wafer W between the two loadingchambers. Also, a portion of the peripheral wall 433 that adjoins themini-environment device 20 and the main housing 30, is formed withaccess ports 436, 437. The housing body 43 of the loader housing 40 iscarried on and supported by the frame structure 331 of the housingsupporting device 33. This prevents the vibrations of the floor frombeing transmitted to the loader housing 40 as well.

[0103] The access port 436 of the loader housing 40 is in alignment withthe access port 226 of the housing 22 of the mini-environment device 20,and a gate valve 27 is provided for selectively blocking a communicationbetween the mini-environment space 21 and the first loading chamber 41.The gate valve 27 has a sealing member 271 which surrounds theperipheries of the access ports 226, 436 and is fixed to the side wall433 in close contact therewith; a door 272 for blocking air from flowingthrough the access ports in cooperation with the sealing material 271;and a driver 273 for moving the door 272. Likewise, the access port 437of the loader housing 40 is in alignment with the access port 325 of thehousing body 32, and a gate valve 45 is provided for selectivelyblocking a communication between the second loading chamber 42 and theworking chamber 31 in a hermetic manner. The gate valve 45 comprises asealing member 451 which surrounds the peripheries of the access ports437, 325 and is fixed to side walls 433, 323 in close contact therewith;a door 452 for blocking air from flowing through the access ports incooperation with the sealing material 451; and a driver 453 for movingthe door 452. Further, the opening formed through the partition wall 434is provided with a gate valve 46 for closing the opening with the door461 to selectively blocking a communication between the first and secondloading chambers in a hermetic manner. These gate valves 27, 45, 46 areconfigured to provide air-tight sealing for the respective chambers whenthey are in a closed state. Since these gate valves may be implementedby conventional ones, detailed description on their structures andoperations is omitted. It should be noted that a method of supportingthe housing 22 of the mini-environment chamber 20 is different from amethod of supporting the loader housing 40. Therefore, for preventingvibrations from being transmitted from the floor through themini-environment chamber 20 to the loader housing 40 and the mainhousing 30, a vibration-absorption damper member may be disposed betweenthe housing 22 and the loader housing 40 to provide air-tight sealingfor the peripheries of the access ports.

[0104] Within the first loading chamber 41, a wafer rack 47 is disposedfor supporting a plurality (two in this embodiment) of wafers spaced inthe vertical direction and maintained in a horizontal state. Asillustrated in FIG. 6, the wafer rack 47 comprises posts 472 fixed atfour corners of a rectangular substrate 471, spaced from one another, inan upright state. Each of the posts 472 is formed with supportingdevices 473, 474 in two stages, such that peripheral edges of wafers Ware carried on and held by these supporting devices. Then, bottoms ofarms of the first and second carrier units, later described, are broughtcloser to wafers from adjacent posts and chuck the wafers.

[0105] The loading chambers 41, 42 can be controlled for the atmosphereto be maintained in a high vacuum state (at a vacuum degree of 10⁻⁵ to10⁶ Pa) by a vacuum evacuator (not shown) in a conventional structureincluding a vacuum pump, not shown. In this event, the first loadingchamber 41 may be held in a low vacuum atmosphere as a low vacuumchamber, while the second loading chamber 42 may be held in a highvacuum atmosphere as a high vacuum chamber, to effectively preventcontamination of wafers. The employment of such a loading housingstructure including two loading chambers allows a wafer W to be carried,without significant delay from the loading chamber the working chamber.The employment of such a loading chamber structure provides for animproved throughput for the defect testing, and the highest possiblevacuum state around the electron source which is required to be kept ina high vacuum state.

[0106] The first and second loading chambers 41, 42 are connected tovacuum pumping pipes and vent pipes for an inert gas (for example, driedpure nitrogen) (neither of which are shown), respectively. In this way,the atmospheric state within each loading chamber is attained by aninert gas vent (which injects an inert gas to prevent an oxygen gas andso on other than the inert gas from attaching on the surface). Since anapparatus itself for implementing the inert gas vent is known instructure, detailed description thereon is omitted.

[0107] In the main housing 30 of the invention using electron beams,when representative lanthanum hexaborate (LaB₆) used as an electronsource for an electro-optical system, later described, is once heated tosuch a high temperature that causes emission of thermal electrons, itshould not be exposed to oxygen within the limits of possibility so asnot to shorten the lifetime. In the invention, the exposure to oxygencan be prevented without fail by carrying out the atmosphere control asmentioned above at a stage before introducing the wafer W into theworking chamber of the main housing in which the electro-optical system70 is disposed.

[0108] Stage apparatus 50

[0109] The stage apparatus 50 comprises a fixed table 51 disposed on thebottom wall 321 of the main housing 30; a Y-table 52 movable in a Ydirection on the fixed table (the direction vertical to the drawingsheet in FIG. 1); an X-table 53 movable in an X direction on the Y-table52 (in the left-to-right direction in FIG. 1); a turntable 54 rotatableon the X-table; and a holder 55 disposed on the turntable 54. A wafer isreleasably held on a wafer carrying surface 551 of the holder 55. Theholder 55 may be of a conventional structure which is capable ofreleasably chucking a wafer by means of a mechanical or electrostaticchuck feature. The stage apparatus 50 uses servo motors, encoders and avariety of sensors (not shown) to operate the above tables to permithighly accurate alignment of a wafer held on the carrying surface 551 bythe holder 55 in the X direction, Y direction and Z-direction (theZ-direction is the up-down direction in FIG. 1) with respect to electronbeams irradiated from the electro-optical system 70, and in a direction(θ direction) about the axis normal to the wafer supporting surface. Thealignment in the Z-direction may be made such that the position on thecarrying surface 551 of the holder 55, for example, can be finelyadjusted in the Z-direction. In this event, a reference position on thecarrying surface is sensed by a position measuring device using a laserof an extremely small diameter (a laser interference range finder usingthe principles of interferometer) to control the position by a feedbackcircuit (not shown). Additionally or alternatively, the position of anotch or an orientation flat of a wafer is measured to sense a planeposition or a rotational position of the wafer relative to the electronbeam to control the position of the wafer by rotating the turntable 54by a stepping motor which can be controlled in extremely small angularincrements. It may be possible to remove the holder 55 and carry a waferW directly on the rotational table. In order to maximally preventparticle produced within the working chamber, servo motors 531, 531 andencoders 522, 532 for the stage apparatus 50 are disposed outside themain housing 30. Since the stage apparatus 50 may be of a conventionalstructure used, for example, in steppers and so on, detailed descriptionon its structure and operation is omitted. Likewise, since the laserinterference range finder may also be of a conventional one, detaileddescription on its structure and operation is omitted.

[0110] It is also possible to establish a basis for signals which aregenerated by previously inputting a rotational position, andX-Y-positions of a wafer relative to the electron beams in a signaldetecting system or an image processing system, later described. Thewafer chucking mechanism provided in the holder 55 is configured toapply a voltage for chucking a wafer to an electrode of an electrostaticchuck, and the alignment is made by pinning three points on the outerperiphery of the wafer (preferably spaced equally in the circumferentialdirection). The wafer chucking mechanism comprises two fixed aligningpins and a push-type clamp pin. The clamp pin can implement automaticchucking and automatic releasing, and constitutes a conducting spot forapplying the voltage.

[0111] While in this embodiment, the X-table is defined as a table whichis movable in the left-to-right direction in FIG. 6(a); and the Y-tableas a table which is movable in the up-down direction, a table movable inthe left-to-right direction in FIG. 2 may be defined as the Y-table; anda table movable in the up-down direction as the X-table.

[0112] Loader 60

[0113] The loader 60 comprises a robot-type first carrier unit 61disposed within the housing 22 of the mini-environment chamber 20; and arobot-type second carrier unit 63 disposed within the second loadingchamber 42.

[0114] The first carrier unit 61 comprises a multi-node arm 612rotatable about an axis O₁-O₁ with respect to a driver 611. While anarbitrary structure may be used for the multi-node arm, the multi-nodearm in this embodiment has three parts which are pivotably attached toeach other. One part of the arm 612 of the first carrier unit 61, i.e.,the first part closest to the driver 611 is attached to a rotatableshaft 613 by a driving mechanism (not shown) of a conventionalstructure, disposed within the driver 611. The arm 612 is pivotableabout the axis O₁-O₁ by means of the shaft 613, and radially telescopicas a whole with respect to the axis O₁-O₁ through relative rotationsamong the parts. At a bottom of the third part of the arm 612 furthestaway from the shaft 613, a chuck 616 in a conventional structure forchucking a wafer, such as a mechanical chuck or an electrostatic chuck,is disposed. The driver 611 is movable in the vertical direction by anelevating mechanism 615 of a conventional structure.

[0115] The first carrier unit 61 extends the arm 612 in either adirection M1 or a direction M2 (FIG. 2) within two cassettes c held inthe cassette holder 10, and removes a wafer accommodated in a cassette cby carrying the wafer on the arm or by chuck bing the wafer with thechuck (not shown) attached at the bottom of the arm. Subsequently, thearm is retracted (in a state as illustrated in FIG. 2), and then rotatedto a position at which the arm can extend in a direction M3 toward theprealigner 25, and stopped at this position. Then, the arm is againextended to transfer the wafer held on the arm to the prealigner 25.After receiving a wafer from the prealigner 25, contrary to theforegoing, the arm is further rotated and stopped at a position at whichit can extend to the second loading chamber 41 (in the direction M4),and transfers the wafer to a wafer receiver 47 within the second loadingchamber 41. For mechanically chuck bing a wafer, the wafer should bechuck bed on a peripheral region (in a range of approximately 5 mm fromthe peripheral edge). This is because the wafer is formed with devices(circuit patterns) over the entire surface except for the peripheralregion, and chuck bing the inner region would result in failed ordefective devices.

[0116] The second carrier unit 63 is basically identical to the firstcarrier unit 61 in structure except that the second carrier unit 63carries a wafer between the wafer rack 47 and the carrying surface ofthe stage apparatus 50, so that detailed description thereon is omitted.

[0117] Each of the first and second carrier units 61, 63 carry a waferfrom a cassette held in the cassette holder 10 to the stage apparatus 50disposed in the working chamber 31 and vice versa, while remainingsubstantially in a horizontal state. The arms of the carrier units 61,63 are moved in the vertical direction only when a wafer is removed fromand inserted into a cassette, when a wafer is carried on and removedfrom the wafer rack, and when a wafer is carried on and removed from thestage apparatus 50. It is therefore possible to smoothly carry a largerwafer, for example, a wafer having a diameter of 30 cm.

[0118] Next, how a wafer is carried will be described in sequence fromthe cassette c held by the cassette holder 10 to the stage apparatus 50disposed in the working chamber 31.

[0119] As described above, when the cassette is manually set, thecassette holder 10 having a structure adapted to the manual setting isused, and when the cassette is automatically set, the cassette holder 10having a structure adapted to the automatic setting is used. In thisembodiment, as the cassette c is set on the up/down table 11 of thecassette holder 10, the up/down table 11 is moved down by the elevatingmechanism 12 to align the cassette c with the access port 225. As thecassette is aligned with the access port 225, a cover (not shown)provided for the cassette is opened, and a cylindrical cover is appliedbetween the cassette c and the access port 225 of the mini-environmentto block the cassette and the mini-environment space 21 from theoutside. Since these structures are known, detailed description on theirstructures and operations is omitted. When the mini-environment device20 is provided with a gate valve for opening and closing the access port225, the gate valve is operated to open the access port 225.

[0120] On the other hand, the arm 612 of the first carrier unit 61remains oriented in either the direction M1 or M2 (in the direction M1in this description). As the access port 225 is opened, the arm 612extends to receive one of wafers accommodated in the cassette at thebottom. While the arm and a wafer to be removed from the cassette areadjusted in the vertical position by moving up or down the driver 611 ofthe first carrier unit 61 and the arm 612 in this embodiment, theadjustment may be made by moving up and down the up/down table 11 of thecassette holder 10, or made by both.

[0121] As the arm 612 has received the wafer, the arm 621 is retracted,and the gate valve is operated to close the access port (when the gatevalve is provided). Next, the arm 612 is pivoted about the axis O₁-O₁such that it can extend in the direction M3. Then, the arm 612 isextended and transfers the wafer carried at the bottom or chucked by thechuck onto the prealigner 25 which aligns the orientation of therotating direction of the wafer (the direction about the central axisvertical to the wafer plane) within a predetermined range. Uponcompletion of the alignment, the carrier unit 61 retracts the arm 612after a wafer has been received from the prealigner 25 to the bottom ofthe arm 612, and takes a posture in which the arm 612 can be extended ina direction M4. Then, the door 272 of the gate valve 27 is moved to openthe access ports 223, 236, and the arm 612 is extended to place thewafer on the upper stage or the lower stage of the wafer rack 47 withinthe first loading chamber 41. It should be noted that before the gatevalve 27 opens the access ports to transfer the wafer to the wafer rack47, the opening 435 formed through the partition wall 434 is closed bythe door 461 of the gate valve 46 in an air-tight state.

[0122] In the process of carrying a wafer by the first carrier unit,clean air flows (as down flows) in laminar flow from the gas supply unit231 disposed on the housing of the mini-environment chamber to preventparticle from attaching on the upper surface of the wafer during thecarriage. A portion of the air near the carrier unit (in thisembodiment, about 20% of the air supplied from the supply unit 231,mainly contaminated air) is aspired from the suction duct 241 of thedischarger 24 and discharged outside the housing. The remaining air isrecovered through the recovery duct 232 disposed on the bottom of thehousing and returned again to the gas supply unit 231.

[0123] As the wafer is placed into the wafer rack 47 within the firstloading chamber 41 of the loader housing 40 by the first carrier unit61, the gate valve 27 is closed to seal the loading chamber 41. Then,the first loading chamber 41 is filled with an inert gas to expel air.Subsequently, the inert gas is also evacuated so that a vacuumatmosphere dominates within the loading chamber 41. The vacuumatmosphere within the loading chamber 41 may be at a low vacuum degree.When a certain degree of vacuum is provided within the loading chamber41, the gate valve 46 is operated to open the access port 434 which hasbeen sealed by the door 461, and the arm 632 of the second carrier unit63 is extended to receive one wafer from the wafer receiver 47 with thechuck at the bottom (the wafer is carried on the bottom or chuck bed bythe chuck attached to the bottom). Upon completion of the receipt of thewafer, the arm 632 is retracted, followed by the gate valve 46 againoperated to close the access port 435 by the door 461. It should benoted that the arm 632 has previously taken a posture in which it canextend in the direction N1 of the wafer rack 47 before the gate valve 46is operated to open the access port 435. Also, as described above, theaccess ports 437, 325 have been closed by the door 452 of the gate valve45 before the gate valve 46 is operated to block the communicationbetween the second loading chamber 42 and the working chamber 31 in anair-tight state, so that the second loading chamber 42 is evacuated.

[0124] As the gate valve 46 is operated to close the access port 435,the second loading chamber 42 is again evacuated at a higher degree ofvacuum than the first loading chamber 41. Meanwhile, the arm 632 of thesecond carrier unit 63 is rotated to a position at which it can extendtoward the stage apparatus 50 within the working chamber 31. On theother hand, in the stage apparatus 50 within the working chamber 31, theY-table 52 is moved upward, as viewed in FIG. 2, to a position at whichthe center line O₀-O₀ of the X-table 53 substantially matches an X-axisX₁-X₁ which passes a pivotal axis O₂-O₂ Of the second carrier unit 63.The X-table 53 in turn is moved to the position closest to the leftmostposition in FIG. 2, and remains awaiting at this position. When thesecond loading chamber 42 is evacuated to substantially the same degreeof vacuum as the working chamber 31, the door 452 of the gate valve 45is moved to open the access ports 437, 325, allowing the arm 632 toextend so that the bottom of the arm 632, which holds a wafer,approaches the stage apparatus 50 within the working chamber 31. Then,the wafer is placed on the carrying surface 551 of the stage apparatus50. As the wafer has been placed on the carrying surface 551, the arm632 is retracted, followed by the gate 45 operated to close the accessports 437, 325.

[0125] The foregoing description has been made on the operation until awafer in the cassette c is carried and placed on the stage apparatus 50.For returning a wafer, which has been carried on the stage apparatus 50and processed, from the stage apparatus 50 to the cassette c, theoperation reverse to the foregoing is performed. Since a plurality ofwafers are stored in the wafer rack 47, the first carrier unit 61 cancarry a wafer between the cassette and the wafer rack 47 while thesecond carrier unit 63 is carrying a wafer between the wafer rack 47 andthe stage apparatus 50, so that the testing operation can be efficientlycarried out.

[0126] Specifically, if an already-processed wafer A and a unprocessedwafer B are placed on the wafer rack 47 of the second carrier unit, (1)the unprocessed wafer B is moved to the stage apparatus 50 and a processfor the wafer B starts. In the middle of this process, (2) the processedwafer A is moved to the wafer rack 47 from the stage apparatus 50. Aunprocessed wafer C is likewise extracted from the wafer rack 47 by thearm and is aligned by the pre-aligner. Then, the wafer C is moved to thewafer rack of the loading chamber 41. By doing so, it is possible toreplace the wafer A with the unprocessed wafer C in the wafer rack 47during the wafer B is being processed.

[0127] Depending upon how such an apparatus for performing a test orevaluation is utilized, a plurality of the stage apparatus 50 can bedisposed to cause a wafer to be transferred from one wafer rack 47 toeach stage apparatus, making it possible to process a plurality ofwafers in a similar manner.

[0128]FIGS. 7A and 7B illustrate an exemplary modification to the methodof supporting the main housing 30. In an exemplary modificationillustrated in FIG. 7A, a housing supporting device 33a is made of athick rectangular steel plate 331 a, and a housing body 32 a is carriedon the steel plate. Therefore, the bottom wall 321 a of the housing body32 a is thinner than the bottom wall 222 of the housing body 32 in theforegoing embodiment. In an exemplary modification illustrated in FIG.7B, a housing body 32 b and a loader housing 40 b are suspended by aframe structure 336 b of a housing supporting device 33 b. Lower ends ofa plurality of vertical frames 337 b fixed to the frame structure 336 bare fixed to four corners of a bottom wall 321 b of the housing body 32b, such that the peripheral wall and the top wall are supported by thebottom wall. A vibration isolator 37 b is disposed between the framestructure 336 b and a base frame 36 b. Likewise, the loader housing 40is suspended by a suspending member 49 b fixed to the frame structure336. In the exemplary modification of the housing body 32 b illustratedin FIG. 7B, the housing body 32 b is supported in suspension, thegeneral center of gravity of the main housing and a variety of devicesdisposed therein can be brought downward. The methods of supporting themain housing and the loader housing are configured to prevent vibrationsfrom being transmitted from the floor to the main housing and the loaderhousing.

[0129] In another exemplary modification, not shown, the housing body ofthe main housing is only supported by the housing supporting device frombelow, while the loader housing may be placed on the floor in the sameway as the adjacent mini-environment chamber. Alternatively, in afurther exemplary modification, not shown, the housing body of the mainhousing is only supported by the frame structure in suspension, whilethe loader housing may be placed on the floor in the same way as theadjacent mini-environment device.

[0130] Electro-optical System 70

[0131] The electro-optical system 70 comprises a column or column 71fixed on the housing body 32. Disposed within the column 71 are anelectro-optical system comprised of a primary electro-optical system(hereinafter simply called the “primary optical system”) and a secondaryelectro-optical system (hereinafter simply called the “secondary opticalsystem”), and a detecting system.

[0132]FIG. 8 shows an embodiment of the electro-optical system 70. Inthe drawing, 72 denotes a primary optical system, 74 a secondary opticalsystem and 76 a detecting system. FIG. 8 also illustrates a stageapparatus 50 carrying a wafer W and a scanning signal generation circuit764 which is a part of a control apparatus. The primary optical system72 irradiates the surface of the sample or wafer W with electron beams,and comprises an electron gun 721 for emitting an electron beam(s); acondenser lens 722 comprised of an electrostatic lens for converging theprimary the electron beam emitted from the electron gun 721; amulti-aperture plate 723 located below the condenser lens 722 and havinga plurality of apertures, for forming a plurality of primary electronbeams or multi-beams from the primary electron beam from the gun 721; areducing lens 724 comprised of an electrostatic lens for reducing theprimary electron beams; a Wien filter or an ExB separator or deflector725; and an objective lens 726. These components are arranged in orderwith the electron gun 721 placed at the top, as illustrated in FIG. 8,and settled such that the optical axes of the electron beams irradiatedare orthogonal to the surface of the wafer W.

[0133] In order to reduce aberration effect of field curvature by thereducing lens 724 and objective lens 726, the multi-apertures 723 a (9apertures in this embodiment) are positioned through the multi-apertureplate 723 such that when the apertures are projected on the X-axis, thedistance Lx between the adjacent points on the X-axis is equal, as shownin FIG. 9A.

[0134] The secondary optical system 74 comprises magnification lenses741, 742 each comprised of an electrostatic lens which pass secondaryelectrons separated from the primary optical system by an ExB deflector725; and a multi-aperture plate 743. A plurality of apertures 743 a ofthe multi-aperture plate 743 are located such that they coincide, one byone, with the apertures 723 a of the multi-aperture plate 723 of theprimary optical system, as illustrated in FIG. 9A.

[0135] The detecting system 76 comprises a plurality of detectors 761 (9detectors in this embodiment) the number of which is equal to that ofthe apertures 743 a of the multi-aperture plate 743 of the secondaryoptical system 74 and located correspondingly thereto; and an imageprocessing section 763 connected through A/D converters 762. The imageprocessing section 763 is not necessary to physically located in theelectro-optical system 70.

[0136] Next, the operation of the electro-optical system 70 configuredas described above will be described. The primary electron beam emittedfrom the electron gun 721 is converged by the condenser lens 722 to forma cross-over at a point P. The primary electron beam which has beenconverged by the condenser lens 722 passes through the apertures 723 aof the multi-aperture plate 723, resulting in that a multiple electronbeams are created. Each of the multi-electron beams is then reduced bythe reducing lens 724 and projected at a point P2. After the focussingat the point P2, the beam passes the objective lens 726 to focus on thesurface of the wafer W. In this situation, the primary electron beamsare deflected by a deflector 727 located between the reducing lens 724and the objective lens 726 to be scanned on the surface of the wafer W.The deflector 727 deflects the primary electron beams in response to ascanning signal applied thereto.

[0137] A method of irradiating primary electron beams by the primaryoptical system 72 will next be explained, with reference to FIG. 9B. Inthe example of FIG. 9B, in order to make explanation brief, four primaryelectron beams 101, 102, 103, 104 are employed. It is assumed that eachof the electron beams is scanned by 50 μm width. As to the beam 101, itscans in the right direction from the left end, returns to the left endimmediately after reaching the right end, and again scans in the rightdirection. Since the four electron beams scan simultaneously on a wafersurface, a throughput can be improved.

[0138] Returning to FIG. 8, a plurality of points on the wafer W areilluminated by a plurality of focussed primary electron beams (ninebeams in the embodiment in FIG. 8), resulting in that secondaryelectrons are emitted from the illuminated points. The secondaryelectrons are then converged by pulling the electric field created bythe objective lens, deflected by the ExB separator 725 to be directed tothe secondary optical system 74. An image created by the secondaryelectrons are focussed at a point P3 which is closer than the point P2.This is because a primary electron has energy of about 500 eV and thesecondary electron has energy of only several eV.

[0139] It will be explained the ExB separator 725 with reference to FIG.10. FIG. 10A illustrates an example of the ExB separator applicable tothe electro-optical apparatus according to the present invention. TheExB separator comprises an electro-static deflector and electromagneticdeflector. FIG. 10 shows a cross sectional view in X-Y planeperpendicular to an optical axis (perpendicular to the drawing surface)OA1. The X and Y-axes are perpendicular to each other.

[0140] The electro-static deflector has a pair of electrodes(electro-static deflection electrodes) 7251 in a vacuum to create aelectric field in the X direction. The electrostatic deflectionelectrodes 7251 are mounted on an inside wall 7253 of the vacuum viaisolation spacers 7252, the distance Dp therebetween is set to besmaller than a length 2L of the electro-static deflection electrodes inthe Y direction. By setting the above, a range where a strength of theelectric field around the Z-axis or the optical axis is substantiallyconstant may be made wide. However, ideally, it is better to set Dp<L tocreate a more wider range having a constant strength electric field.

[0141] In particular, the strength of the electric field is not constantin a range of Dp/2 from the end of the electrode. Therefore, the rangewhere a strength of the electric field is constant is represented by2L-Dp which is a center potion of the electrode, excluding thenon-constant regions. Accordingly, in order to create a range where thestrength electric field is constant, it is necessary to settle tosatisfy 2L>Dp, and it is more preferable to set L>Dp to create a broaderrange thereof. The electromagnetic deflector for creating a magneticfield in the Y direction is provided outside the vacuum wall 7253. Theelectromagnetic deflector comprises electromagnetic coils 7254, 7255,which generate magnetic fields in the X and Y directions. Although onlythe coil 7255 can provide the magnetic field in the Y direction, thecoil for generating the magnetic field in the X direction is alsoprovided to improve the perpendicular character between the electric andmagnetic fields. Namely, the component in the −X direction of themagnetic field created by the coil 7254 cancels the component in the +Xdirection created by the coil 7255 to obtain the improved perpendicularcharacter between the electric and magnetic fields.

[0142] Each of the coils for generating the magnetic field consists oftwo parts to be installed outside the vacuum wall, which are mounted onthe surface of the vacuum wall 7253 from the both sides thereof, andfixedly clamped at portions 7257 with screws or the like.

[0143] The most outer layer 7256 of the ExB separator is formed as yokesmade of Permalloy or ferrite. The most outer layer 7256 consists of twoparts, and are mounted on the outer surface of the coil 7255 and fixedlyclamped at portions 7257 with screws or the like.

[0144]FIG. 10B illustrates another example of the ExB separatorapplicable to the electro-optical system 70 according to this invention,with a cross sectional view perpendicular to an optical axis. This ExBseparator is different to the example shown in FIG. 10A in the point ofview that it includes six electro-static deflection electrodes 7251. InFIG. 10B, components of the ExB separator corresponding to those of FIG.10A are denoted by the same reference numerals with “′”, and descriptionthereof is omitted. The electro-static deflection electrodes 7251′ aresupplied with the voltages k*cosθi (k: constant value), where θi (i=0,1, 2, 3, 4, 5) is an angle between a line from the electrode center tothe optical axis and the electric field direction (X direction)

[0145] The ExB separator illustrated in FIG. 10B has coils 7254′, 7255′for generating magnetic fields in the X and Y directions to control theperpendicular character, similar to that in FIG. 10A.

[0146] The ExB separator shown in FIG. 10B can provide a wider rangewhere the electric field strength is constant, in comparison with thatin FIG. 10A.

[0147] The coils for generating the magnetic fields are of asaddle-shaped type in the ExB separators illustrated in FIGS. 10A and10B. However, a coil of a troidal type can also be employed. Further,the ExB separators shown in FIG. 10 can be applied to embodiments of theelectron beam apparatuses explained below as well as the electron beamapparatus 70 shown in FIG. 8.

[0148] Returning to FIG. 8, the images of the secondary electron beamsfocussed at the point P3 are again focussed at respective correspondingapertures 743 a of the multi-aperture detection plate 743 by through theenlarging lenses 741, 742, and detected the detectors 761correspondingly located to the apertures 743 a. The detectors 761convert the detected beams to electric signals representing the strengthof the beams. The electric signals are converted to digital signals atthe A/D converters 762 and inputted to the image processing unit 763. Asthe detectors 761, PN junction diodes which directly detect strengths ofelectron beams, PMT (photo multiplier tubes) which detect strengths ofelectron beams after converting them to radiation light by a fluorescentplate.

[0149] The image processing unit 763 provides image data obtained fromthe input digital data. The image processing unit 763 receives ascanning signal which is used to deflect the primary electron beams,from the control unit 2 (FIG. 1). Therefore, the image processing unitreceives a signal representing positions of irradiated points on thewafer, and hence can produce an image representing the wafer surface. Bycomparing the image obtained as above with a predetermined referencepattern, the quality of the pattern on the wafer to be evaluated isdetermined.

[0150] Further, by moving the pattern on the wafer to be evaluated to aposition near the optical axis of the primary optical system byregistration, obtaining a line width evaluation signal by line-scanning,and by calibrating it, a line width of a pattern on the wafer surfacecan be detected.

[0151] In a prior electron beam apparatus, secondary electrons which aregenerated when primary electron beams are irradiated on a wafer, arefocussed to a point via two steps lenses common to the primaryelectrons, are deflected by an ExB separator 725 located at the focalpoint, and are imaged at multiple detectors without passing any lens. Asto the common lenses of the primary and secondary optical systems, sinceit is required to adjust a lens conditions of the primary optical systemprior to that of the secondary optical system, a focal condition andenlarging rate of the secondary optical system cannot be controlled.Therefore, the focal condition and enlarging rate thereof cannot besufficiently adjusted when they are incorrect.

[0152] On the other hand, in the present invention, after the secondaryelectrons are deflected by the ExB separator 725, they are enlarged bythe lens of the secondary optical system, a focal condition andenlarging rate can be adjustable apart from a lens condition setting ofthe primary optical system.

[0153] After the primary electron beams pass through the apertures ofthe multi-aperture plate 723 of the primary optical system, they arefocussed on the wafer W, and thereby the secondary electrons are emittedfrom the wafer. The secondary electron beams are then imaged at thedetectors 761. In this event, it is necessary to minimize threeaberration effects which are distortion, axial chromatic aberration, andfield astigmatism derived in the primary optical system.

[0154] In particular, in the case where optical paths of the primary andsecondary electron beams are partially common, since primary electronstreams and secondary electron streams flow through the common opticalpath, a beam current having 2 times flows, and thus peculiar in thefocal condition of the primary electron beam caused by a space chargeeffect is two times. Also, it is difficult to adjust the axes of theprimary and secondary electron beams in the common optical path. Thatis, when an adjustment of the axis of the primary electron beams, theaxis of the secondary electron beams may be out of their condition, andwhen an adjustment of an axis of the secondary electron beams, the axisof the primary electron beams may be out of their condition. Further, inthe common optical path, when the lens is adjusted to satisfy a focalcondition of the primary electron beams, a focal condition of thesecondary electron beams may be out of the condition, and the focalcondition of the secondary electron beams is adjusted, the focalcondition of the primary electron beams may be out of the condition.

[0155] Therefore, it is better to design the common path as short aspossible. However, when an ExB separator 725 is installed at a positionunder an objective lens 726, this occurs a problem that an image plandistance of the objective lens is longer, and thereby aberrations arelarger. In the present invention, the ExB separator 725 is installed ata side of the electron gun 721 with respect to the objective lens,resulting in that the primary and secondary optical systems commonlyemploy only a single lens.

[0156] In addition, as to relationships between spaces among the primaryelectron beams and the secondary optical system, when the primaryelectron beams are spaced to each other by a distance larger than theaberration of the secondary optical system to reduce cross-talk betweenthe beams.

[0157] Further, it is preferable to set an deflection angle of theelectro-static deflector 727 to be −½ of an electromagnetic deflectionangle by the electromagnetic deflector of the ExB separator 725. Sincethe chromatic aberration of deflection may be small by setting above, abeam diameter of the beam may be made relatively small even the beampasses the ExB separator.

[0158] Pre-charge Unit 81

[0159] The pre-charge unit 81, as illustrated in FIG. 1, is disposedadjacent to the column 71 of the electro-optical system 70 within theworking chamber 31. Since this evaluation system 1 is configured to testa wafer for device patterns or the like formed on the surface thereof byirradiating the wafer with electron beams, the surface of the wafer maybe charged up depending on conditions such as the wafer material, energyof the irradiated electrons, and so on. Further, even on the surface ofa single wafer, some regions may be highly charged, while the otherregions may be lowly charged. Variations in the amount of charge on thesurface of the wafer would cause corresponding variations in informationprovided by the resulting secondary electrons, thereby failing toacquire correct information. For preventing such variations, in thisembodiment, the pre-charge unit 81 is provided with a charged particleirradiating unit 811. Before testing electrons are irradiated to apredetermined region on a wafer, charged particles are irradiated fromthe charged particle irradiating unit 811 of the pre-charge unit 81 toeliminate variations in charge. The charges on the surface of the waferpreviously form an image of the surface of the wafer, which image isevaluated to detect possible variations in charge to operate thepre-charge unit 81 based on the detection. Alternatively, the pre-chargeunit 81 may irradiate a blurred primary electron beam.

[0160] In a method of detecting an electrical defect of a wafer, it iscapable to utilize such a phenomenon that when there are electricallyisolated and conductive portions on the wafer, voltages of the portionsare different to each other. In order that, a wafer is pre-charged tocause a difference in potential between portions which are intended tobe electrically isolated, provided that one of them is conductive infact, and then electron beams are irradiated on the wafer to detect thevoltage difference therebetween. By analyzing the detected data, theconductive portion which is intended to be isolated can be detected.

[0161] In such a method of detecting an electrical defect, thepre-charge unit 81 can be employed to pre-charge a wafer.

[0162] Potential Applying Unit 83

[0163]FIG. 11 shows a constitution of the potential applying mechanism83. The mechanism 83 applies a potential of±several volts to a carrierof a stage, on which the wafer is placed, to control the generation ofsecondary electrons based on the fact that the information on thesecondary electrons emitted from the wafer (secondary electron yield)depend on the potential on the wafer. The potential applying mechanism83 also serves to decelerate the energy originally possessed byirradiated electrons to provide the wafer with irradiated electronenergy of approximately 100 to 500 eV.

[0164] As illustrated in FIG. 11, the potential applying mechanism 83comprises a voltage applying device 831 electrically connected to thecarrying surface 551 of the stage apparatus 50; and a charge-upexamining/voltage determining system (hereinafter examining/determiningsystem) 832. The examining/determining system 832 comprises a monitor833 electrically connected to an image processing unit 763 of thedetecting system 76 in the electro-optical system 70; an operator 834connected to the monitor 833; and a CPU 835 connected to the operator834. The CPU 835 is incorporated in the control unit 2 (FIG. 1), andsupplies a voltage control signal to the voltage applying device 831.The CPU 835 further provides some components of the electron system withcontrol signals. For instance, it applies a scanning signal to thedeflector 727 (FIG. 8) of the electro-optical system 70. In thepotential applying mechanism 83, the monitor 833 displays an imagereproduced by the image processing unit 763. By studying the image, anoperator can search, using an operation input unit 834 and CPU 835, apotential at which the wafer is hardly charged, and control thepotential applying device 831 to provide the potential to the holder 55of the stage apparatus 50.

[0165] Electron Beam Calibration Mechanism 85

[0166] As illustrated in FIGS. 12A and 12B, the electron beamcalibration mechanism 85 comprises a plurality of Faraday cups 851, 852for measuring a beam current, disposed at a plurality of positions in alateral region of the wafer carrying surface 541 on the turntable 54.The Faraday cups 851 are provided for a narrow beam (approximately φ=2μm), while the Faraday cups 852 for a wide beam (approximately φ=30 μm).The Faraday cuts 851 for a narrow beam measure a beam profile by drivingthe turntable 54 step by step, while the Faraday cups 852 for a widebeam measure a total amount of currents. The Faraday cups 851, 852 aremounted on the wafer carrying surface 541 such that their top surfacesare coplanar with the upper surface of the wafer W carried on thecarrying surface 541. In this way, the primary electron beam emittedfrom the electron gun is monitored at all times, and a voltage to theelectron gun is controlled so that the strength of the electron beamsapplied at the wafer W is substantially constant. That is, sinceelectron guns cannot emit a constant electron beams at all times butvaries in the emission current as it is used over time, the electronbeam strength is calibrated by the calibration mechanism.

[0167] Alignment Controller 87

[0168] The alignment controller 87 aligns the wafer W with theelectro-optical system 70 using the stage apparatus 50. The alignmentcontroller 87 performs the control for rough alignment through widefield observation using the optical microscope 871 (a measurement with alower magnification than a measurement made by the electro-opticalsystem); high magnification alignment using the electro-optical systemof the electro-optical system 70; focus adjustment; testing regionsetting; pattern alignment; and so on. The wafer is tested at a lowmagnification in this way because an alignment mark must be readilydetected by an electron beam when the wafer is aligned by observingpatterns on the wafer in a narrow field using the electron beam forautomatically testing the wafer for patterns thereon.

[0169] The optical microscope 871 is disposed on the housing 30.Alternatively, it may be movably disposed within the housing 30. A lightsource (not shown) for operating the optical microscope 871 isadditionally disposed within the housing 30. The electro-optical systemfor observing the wafer at a high magnification, shares theelectro-optical systems (primary optical system 72 and secondary opticalsystem 74) of the electro-optical system 70.

[0170] The configuration of the alignment controller 87 may be generallyillustrated in FIG. 13. For observing a point of interest on a wafer ata low magnification, the X-stage or Y-stage of the stage apparatus 50 iscontrolled to move the point of interest on the wafer into a field ofthe optical microscope 871. The wafer is studied in a wide field by theoptical microscope 871, and the point of interest on the wafer to beobserved is displayed on a monitor 873 through a CCD 872 to roughlydetermine a position to be observed. In this event, the magnification ofthe optical microscope may be changed from a low magnification to a highmagnification.

[0171] Next, the stage apparatus 50 is moved by a distance correspondingto a spacing δx between the optical axis of the electro-optical system70 and the optical axis of the optical microscope 871 to move the pointon the wafer under observation, previously determined by the opticalmicroscope 871, to a point in the field of the electro-optical system70. In this event, since the distance δx between the axis O₃-O₃ of theelectro-optical system and the axis O₄-O₄ of the optical microscope 871is previously known (while it is assumed that the electro-optical system70 is deviated from the optical microscope 871 in the direction alongthe X-axis in this embodiment, they may be deviated in the Y directionas well as in the X direction), the point under observation can be movedto the viewing position by moving the stage apparatus 50 by the distanceδx. After the point under observation has been moved to the viewingposition of the electro-optical system 70, the point under observationis imaged by the electro-optical system at a high magnification forstoring a resulting image or displaying the image on the monitor 765.

[0172] After the point under observation on the wafer imaged by theelectro-optical system at a high magnification is displayed on themonitor, misalignment of the stage apparatus 50 with respect to thecenter of rotation of the turntable 54 in the wafer rotating direction,or misalignment δθ of the wafer in the wafer rotating direction withrespect to the optical axis O₃-O₃ of the electro-optical system 70 aredetected in a conventional method. Then, the operation of the stageapparatus 50 is controlled to align the wafer, based on the detectedvalues and data on a testing mark attached on the wafer, or data on theshape of the patterns on the wafer which have been acquired inseparation.

[0173] Controller 2

[0174] The controller mainly comprises a main controller, a controlcontroller and a stage controller.

[0175] The main controller has a man-machine interface through which theoperation by an operator (input of various instructions/commands andmenus, instruction to start a test, switch between automatic and manualtest modes, input of all commands necessary when the manual test mode)is performed. Further, the main controller performs a communication to ahost computer in a factory, control of a vacuum pumping system, carriageof a sample such as a wafer, control of alignment, transmission ofcommands to the control controller and the stage controller and receiptof information. Moreover, the main controller has a function ofobtaining an image signal from the optical microscope, a stage vibrationcorrecting function for feeding back a vibration signal of the stage tothe electro-optical system to correct a deteriorated image, and anautomatic focus correcting function for detecting a Z-direction (thedirection of the axis of the primary optical system) displacement of asample observing position to feed back the displacement to theelectro-optical system so as to automatically correct the focus.Reception and transmission of a feedback signal to the electro-opticalsystem and a signal from the stage can be performed through the controlcontroller and the stage controller.

[0176] The control controller is mainly responsible for control of theelectro-optical system, or control of highly accurate voltage sourcesfor electron gun, lenses, aligner and Wien filter). Specifically, thecontrol controller effects control (gang control) of automatic voltagesetting to each lens system and the aligner in correspondence with eachoperation mode, for example, causes a region to be irradiated by aconstant electron current even if the magnification is changed, andautomatically sets a voltage applied to each lens system and the alignerin correspondence with each magnification.

[0177] The stage controller is mainly responsible for control regardingthe movement of the stage and enables the achievement of accurate X andY direction movements of micrometer order (tolerance: ±0.5 micrometer).Further, the stage controller achieves control of rotation (θ control)of the stage within an error accuracy of ±0.3 seconds.

[0178] The evaluating system according to the invention as describedabove, can functionally combine the electron beam apparatus of amulti-beam type with the respective components of the evaluation system,resulting in that samples can be evaluated with a high throughput. If asensor for detecting a clean level of the environment housing, it ispossible to test samples while monitoring refuses in the housing.Further, since the pre-charge unit is provided, a wafer made of aninsulation material may not be affected from charging.

[0179] Some embodiments of a combination of a stage apparatus 50 and acharged particle beam irradiation portion of a electro-optical system 70in the electron beam apparatus accommodated in the evaluation system 1according to the present invention.

[0180] When testing a sample such as a semiconductor wafer possessedwith ultra accurate processing, a stage apparatus 50 which is capable ofaccurately positioning the wafer in a vacuum working chamber 31, isrequired. As such a stage apparatus usable in such a case that ultraaccurately positioning is required, a mechanism for supporting X-Y stagewith a hydrostatic bearings with a non-contact manner, is employed. Inthis event, a degree of vacuum is maintained in the vacuum chamber orworking chamber 31 by forming a differential pumping mechanism forpumping a high pressure gas in a range of the hydrostatic bearing sothat the high pressure gas supplied from the hydrostatic bearings willnot be pumped directly to the working chamber 31. In the description,the term “vacuum” means a vacuum condition so-called in this field.

[0181] An example of the combination of a stage apparatus andelectro-optical system 70 according to the prior art is illustrated inFIG. 14. FIGS. 14A and 14B are elevation and side views, respectively.In the prior art, a bottom of a column 71 of an electron beam apparatusfor generating an electron beam to irradiate a wafer, i.e., an electronbeam emitting tip 72 is attached to a main housing 30 which constitutesa vacuum chamber 31. The inside of the column 71 is evacuated to vacuumby a vacuum pipe 10-1, and the chamber 31 is evacuated to a vacuum by avacuum pipe 11-1 a. Then, electron beam is emitted from the bottom 72 ofthe column 71 to a sample such as a wafer W placed therebelow.

[0182] The wafer W is removably held on a holder 55 in a known method.The holder 55 is mounted on the top surface of a Y-table 52 of an X-Ystage. The Y-table 52 has a plurality of hydrostatic bearings 9-1attached on surfaces (both left and right side surfaces and a lowersurface in FIG. 14A) opposite to a guide surface of an X-table 53. TheY-table 52 is movable in the Y direction (in the left-to-right directionin FIG. 12B), while maintaining a small gap between the guide surfaceand the opposite surfaces by the action of the hydrostatic bearings 9-1.Further, around the hydrostatic bearings 9-1, a differential pumpingmechanism is disposed to prevent a high pressure gas supplied to thehydrostatic bearings 9-1 from leaking into the inside of the vacuumchamber 31. This situation is shown in FIG. 15.

[0183] As illustrated in FIG. 15, double grooves 18-1 and 17-1 areformed around the hydrostatic bearings 9-1, and these grooves areevacuated to vacuum at all times by a vacuum pipe and a vacuum pump, notshown. With such a structure, the Y-table 52 is supported in anon-contact state in vacuum so that it is freely movable in the Ydirection. These double grooves 18-1 and 17-1 are formed to surround thehydrostatic bearings 9-1 of the Y-table 52, on the surface on which thehydrostatic bearings are disposed. Since the hydrostatic bearing mayhave a known structure, detailed description thereon is omitted.

[0184] The X-table 53, which carries the Y-table 52 has a concave shapeopen directed upwardly, as is apparent from FIG. 14. The X-table 53 isalso provided with completely similar hydrostatic bearings and grooves,such that the X-table 53 is supported to a stage stand or fixed table 51in a non-contact manner, and is freely movable in the X direction.

[0185] By combining movements of these Y-table 52 and X-table 53, it ispossible to move the wafer W to an arbitrary position in the horizontaldirection with respect to the bottom of the column, i.e., the electronbeam emitting tip 72 to emit electron beams to a desired position of thewafer W.

[0186] In the combination of the stage apparatus 50 and the electronbeam emitting tip 72 can be employed in the evaluation system accordingto the present invention. However, there are problems below.

[0187] In the prior combination of the hydrostatic bearings 9-1 and thedifferential pumping mechanism, the guide surfaces 53 a, 51 a opposingto the hydrostatic bearings 9-1 reciprocate between a high pressure gasatmosphere around the hydrostatic bearings and a vacuum environmentwithin the working chamber 31 as the X-Y stage is moved. In this event,while the guide surfaces are exposed to the high pressure gasatmosphere, the gas is adsorbed to the guide surfaces, and the adsorbedgas is released as the guide surfaces are exposed to the vacuumenvironment. Such states are repeated. Therefore, as the X-Y stage ismoved, the degree of vacuum within the working chamber 31 is degraded,rising a problem that the aforementioned processing such as exposure,testing and working, by use of the electron beam cannot be stablyperformed and that the wafer is contaminated.

[0188] Therefore, an apparatus is required which prevents the degree ofvacuum from degrading to permit stable processing such as testing andworking by use of an electron beam. FIG. 16 shows an embodiment of thecombination of the stage apparatus 50 and the electron beam emitting tip72 of an electro-optical system 70, which can derive advantages above.In FIG. 16, FIGS. 16A and 16B are front and side views, respectively.

[0189] As illustrated in FIG. 16, a partition plate 14-1 largelyextending substantially horizontally in the ±Y directions (in the leftand right directions in FIG. 16B) is attached on the top surface of aY-table 52, such that a reducer 50-1 having a small conductance isformed at all times between the top surface of the X-table 53 and thepartition plate 14-1. Also, on the top surface of an X-table 53, apartition plate 12-1 is placed to extend in the +X directions (in theleft and right directions in FIG. 14A), such that a reducer 51-1 isformed at all time between the top surface of a fixed table 51 and thepartition plate 12-1. The fixed table 51 is mounted on a bottom wall ina main housing 30 in a conventional manner.

[0190] Thus, since the reducers 50-1 and 51-1 are formed at all timeswhen the wafer table or holder 55 is moved to whichever position, sothat even if a gas is released from the guide surfaces 53 a and 51 awhile the Y-table 52 and X-table 53 are moved, the movement of thereleased gas is prevented by the reducers 50-1 and 51-1. Therefore, itis possible to significantly suppress an increase in pressure in a space24-1 near the wafer irradiated with electron beams.

[0191] The side and lower surfaces of the movable section or Y-table 52and the lower surface of the X-table 53 of the stage apparatus 50 areformed with grooves, around the hydrostatic bearings 9-1, fordifferential pumping, as illustrated in FIG. 15. Since evacuation tovacuum is performed through these grooves, the released gas from theguide surfaces are mainly pumped by these differential pumping mechanismwhen the reducers 1550, 1551 are formed. Therefore, the pressures in thespaces 13-1 and 15-1 within the stage apparatus 50 are higher than thepressure within the working chamber 30. Therefore, if locations whichare evacuated to vacuum are separately provided, not only the spaces13-1 and 15-1 are evacuated through the differential pumping grooves17-1 and 18-1, but also the pressures in the spaces 13-1 and 15-1 can bereduced to further suppress an increase in pressure near the wafer W.Vacuum evacuation passages 11-1 b and 11-lc are provided for thispurpose. The evacuation passage 11-1 b extends through the fixed table51 and the main housing 30 and communicates with the outside of thehousing 30. The evacuation passage 11-1 c is formed in the X-table 53and opened to the lower surface of the X-table.

[0192] While the provision of the partition plates 12-1 and 14-1 resultsin a requirement of increasing the size of the working chamber 30 suchthat the chamber 30 does not interfere with the partition walls, thisaspect can be improved by making the partition plates of a retractilematerial or in a telescopical structure. In such an improved embodiment,the partition wall is made of rubber or in bellows form, and its end inthe moving direction is fixed to the X-table 53 for the partition plate14-1, and to an inner wall of the housing 8 for the partition plate12-1, respectively.

[0193]FIG. 17 illustrates another embodiment of the combination of thestage apparatus 50 and the electron emitting tip 72 of theelectro-optical system 70. In the example, a cylindrical partition 16-1is formed around the bottom of the column 71, i.e., the electron beamemitting tip 72 to provide a reducer between the top surface of thewafer W and the electron beam emitting tip 72. In such a configuration,even if a gas is released from the X-Y stage to cause an increasedpressure within the working chamber 31, a pressure difference isproduced between the inside of the chamber C and the inside 1524 of thepartition, because the inside 24-1 of the partition is partitioned bythe partition 16-1 and the gas is pumped through the vacuum pipe 10-1.Therefore, an increased pressure within the space 24-1 in the partitionmay be suppressed. While a gap between the partition 16-1 and thesurface of the wafer W should be settled depending on the pressuremaintained within the working chamber 31 and around the emitting tip 72,approximately several tens of μm to several mm are proper. The inside ofthe partition 16-1 is communicated with the vacuum pipe 10-1 by aconventional method.

[0194] Also, since electron beam apparatus may apply a wafer W with ahigh voltage of approximately several kV, a conductive material placednear the wafer gives rise to a discharge. In this case, the partition16-1 may be made of an insulating material such as ceramics to prevent adischarge between the wafer W and the partition 16-1.

[0195] A ring member 4-1 disposed around the wafer W is a plate-shapedadjusting part fixed to the wafer base or holder 55, which is set at thesame level as the wafer such that a small gap 25-1 is formed over theentire periphery of the bottom of the partition 16-1. Therefore, evenwhen electron beams are irradiated to whichever position of the wafer W,the constant small gap 52-1 is formed at all times at the bottom of thepartition 16-1, thereby making it possible to stably maintain thepressure in the space 24-1 around the bottom of the column 71.

[0196]FIG. 18 illustrates a still another embodiment of the combinationof the stage apparatus 50 and the electron beam emitting tip 72 of theelectron beam apparatus. A partition 19-1 containing a differentialpumping structure is disposed around an electron beam emitting tip 72 ofthe column 71. The partition 19-1 has a cylindrical shape, and acircumferential groove 20-1 is formed inside. An pumping passage 21-1extends upward from the circumferential grove. The pumping passage isconnected to a vacuum pipe 23-1 through an internal space 22-1. There isa small gap ranging from several tens of μm to several mm between thelower end of the partition wall 19-1 and the upper surface of the waferW.

[0197] In the configuration shown in FIG. 18, even if a gas is releasedfrom the stage apparatus 50 in association with a movement of the X-Ystage to cause an increased pressure within a working chamber 30, andthe gas is going to flow into the electron beam emitting tip 72, thepartition 19-1 reduces the gap between the wafer W and the tip to makethe conductance extremely small. Therefore, the gas is impeded fromflowing into the electron beam emitting tip 72 and the amount of flowinggas is reduced. Further, the introduced gas is pumped from thecircumferential groove 20-1 to the vacuum pipe 1523, so thatsubstantially no gas flows into the space 24-1 around the electron beamemitting tip 72, thereby making it possible to maintain the pressurearound the electron beam emitting tip 72 at a desired high vacuum.

[0198]FIG. 19 illustrates another embodiment of the combination of thestage apparatus 50 and the electron beam emitting tip 72 of theelectro-optical system 70. In this embodiment, a partition 26-1 isformed around the electron beam emitting tip 72 in the working chamber31 to separate the electron beam emitting tip 72 from the chamber 31.This partition 26-1 is coupled to a freezer 30-1 through a supportingmember 29-1 made of a high thermally conductive material such as copperor aluminum, and is cooled at −100° C. to −200° C. A member 27-1 isprovided for preventing thermal conduction between the cooled partition26-1 and the column 71, and is made of a low thermally conductivematerial such as ceramics resin material. Also, a member 28-1, which ismade of a non-insulating material such as ceramics, is formed at a lowerend of the partition 26-1 for preventing the wafer W and the partition26-1 from discharging therebetween.

[0199] In the configuration shown in FIG. 19, gas molecules which aregoing to flow from the working chamber 31 into the electron beamemitting tip 72 are impeded by the partition 26-1 from flowing towardthe electron beam emitting tip, and even if the molecules flow, they arefrozen and trapped on the surface of the partition 26-1, thereby makingit possible to maintain low the pressure in the space around theelectron beam emitting tip 72.

[0200] As the freezer, a variety of freezers can be used such as aliquid nitrogen based freezer, an He freezer, a pulse tube type freezer,and so on.

[0201]FIG. 20 illustrates a further embodiment of the combination of thestage apparatus 50 and the electron beam emitting tip 72 of theelectro-optical system 70. Similar to the constitution shown in FIG. 16,a partition plates 12-1, 14-1 are disposed on both movable sections ofthe X-Y stage or Y and X-tables 52, 53. Therefore, even if the samplebase or holder 55 is moved to an arbitrary position, the space 13-1within the stage apparatus and the inside of the working chamber 31 arepartitioned by these partitions through reducers 50-1, 51-1. Further, apartition 16-1 similar to that illustrated in FIG. 17 is formed aroundthe electron beam emitting tip 72 to partition the inside of the workingchamber 31 and the space 24-1, in which the electron beam emitting tip72 is positioned, through a reducer 52-1. Therefore, even if a gasadsorbed on the stage is released into the space 13-1 while the stage ismoved, to increase the pressure in this space, an increased pressure inthe working chamber 31 is suppressed, and an increased pressure in thespace 24-1 is further suppressed. In this way, the pressure in the space24-1 around the electron beam irradiation tip 71 can be maintained in alow state. In addition, the space 24-1 can be stably maintained at a yetlower pressure, by utilizing the partition 19-1 which contains adifferential pumping mechanism, or the partition 26-1 cooled by afreezer which is illustrated in FIG. 40, as the partition 16-1.

[0202] In this embodiment with regard to the electron beam emitting tip,the stage apparatus can be accurately positioned in the vacuumed workingchamber, and the pressure around the irradiation tip is prevented fromincreasing, resulting in obtaining a high quality image data.

[0203]FIG. 21 shows a more further embodiment of the combination of thestage apparatus 50 and the electron beam emitting tip 72 of theelectro-optical system 70. In this embodiment, a bottom of the column71, i.e., the electron beam emitting tip 72 is attached to a mainhousing 30 which defines a working chamber 31. A base or fixed table ofthe X-Y stage of the stage apparatus 50 is fixed on a bottom wall of themain housing 30, and a Y-table 52 is mounted on the fixed table 51. Onboth sides of the Y-table 52 (on left and right sides in FIG. 21),protrusions are formed, which are protruding into recessed grooves of apair of Y direction guides 7 a-2 and 7 b-2 carried on the fixed table 51formed in the sides facing the Y-table. The recessed grooves extend inthe Y direction (the direction perpendicular to the drawing surface)substantially over the entire length of the Y direction guides.Hydrostatic bearings 11 a-2, 9 a-2, 11 b-2, 9 b-2 in a known structureare disposed on the top surface, bottom surface and side surfaces of theprotrusions protruding into the recessed grooves, respectively. A highpressure gas is blown off through these hydrostatic bearings to supportthe Y-table 52 with respect to the Y direction guides 7 a-2, 7 b-2 in anon-contact manner and to allow the same to smoothly reciprocate in theY direction. Also, a linear motor 12-2 in a known structure is disposedbetween the pedestal table 51 and the Y-table 52 to drive the Y-table inthe Y direction. The Y-table 52 is supplied with a high pressure gasthrough a flexible pipe 22-2 for high pressure gas supply, so that thehigh pressure gas is supplied to the hydrostatic bearings 9 a-2 to 11a-2 and 9 b-2 to 11 b-2 through a gas passage (not shown) formed in theY-table. The high pressure gas supplied to the hydrostatic bearingsblows out into a gap of several microns to several tens of micronsformed between opposing guiding surfaces of the Y direction guide toserve to precisely position the Y-table 52 with respect to the guidesurfaces in the X direction and Z-direction (upward and downwarddirections in FIG. 21).

[0204] An X-table 53 is carried on the Y-table 52 for movement in the Xdirection (in the left-to-right direction in FIG. 21). On the Y-table52, a pair of X direction guides 8 a-2, 8 b-2 (only 8 a-2 is shown)identical in structure to the Y direction guides 7 a-2, 7 b-2 for theY-table are disposed with the X-table 53 interposed therebetween. Arecessed groove is also formed in the side of the X direction guidefacing the X-table 53, and a protrusion is formed in a side portion ofthe X-table (a side portion facing the X direction guide), protrudinginto the recessed groove. The recessed groove extends substantially overthe entire length of the X direction guide. Hydrostatic bearings (notshown) similar to the hydrostatic bearings 11 a-2, 9 a-2, 10 a-2, 11b-2, 9 b-2, 10 b-2 are disposed on the top surface, bottom surface andside surfaces of the protrusion of the X-table 53 protruding into therecessed groove in similar positioning. Between the Y-table 52 and theX-table 53, a linear motor 13-2 in a known structure is disposed so thatthe X-table is driven in the X direction by means of the linear motor.Then, the X-table 53 is supplied with a high pressure gas through aflexible pipe 21-2 to supply the high pressure gas to the hydrostaticbearings. The high pressure gas is blown out from the hydrostaticbearings to the guide surfaces of the X direction guide to highlyaccurately support the X-table 53 with respect to the Y direction guidein a non-contact manner. The vacuum working chamber 31 is evacuated byvacuum pipes 19-2, 20 a-2, 20 b-2 connected to a vacuum pump or the likein a conventional structure. The inlet sides (within the workingchamber) of the pipes 20 a-2, 20 b-2 extend through the pedestal orfixed table 51 and are open near a position at which the high pressuregas is pumped from the X-Y stage on the top surface of the table 51, tomaximally prevent the pressure within the working chamber 31 from risingdue to the high pressure gas blown out from the hydrostatic bearings.

[0205] A differential pumping mechanism 25-2 is disposed around theelectron beam emitting tip 72, so that the pressure in the electron beamirradiation space 30-2 is held sufficiently low even if the pressure inthe working chamber 31 is high. Specifically, an annular member 26-2 ofthe differential pumping mechanism 25-2 attached around the electronbeam emitting tip 72 is positioned with respect to the main housing 30such that a small gap (from several micron to several hundred microns)40-2 is formed between the lower surface (the surface opposing the waferW) and the wafer, and an annular groove 27-2 is formed on the lowersurface thereof. The annular groove 27-2 is connected to a vacuum pumpor the like, not shown, through an pumping pipe 28-2. Therefore, thesmall gap 40-2 is evacuated through the annular groove 27-2 and anevacuate port 28-2, so that even if gas molecules attempt to invade fromthe working chamber 31 into the electron beam irradiating space 30-2surrounded by the annular member 1626, they are pumped. In this way, thepressure within the electron beam irradiation space 30-2 can be held lowto irradiate an electron beam without problem.

[0206] The annular groove 27-2 may be in a double structure or in atriple structure depending on the pressure within the chamber or thepressure within the electron beam irradiation space 30-2.

[0207] For the high pressure gas supplied to the hydrostatic bearings,dry nitrogen is generally used. However, if possible, a highly pureinert gas is further preferable. This is because if impurities such asmoisture and oil components are included in the gas, these impuritymolecules will attach on the inner surface of the housing which definesthe vacuum chamber, and on the surfaces of components of the stage todeteriorate the degree of vacuum, and will attach on the surface of thesample to deteriorate the degree of vacuum in the electron beamirradiation space.

[0208] In the foregoing description, the sample or wafer W is notgenerally carried directly on the X-table 53, but carried on a waferbase or holder which has functions of removably holding the wafer, andmaking a slight positional change with respect to the X-Y stage, and soon. However, since the presence or absence of the sample base, and itsstructure are not related to the gist of the present invention, they areomitted for simplifying the description.

[0209] Since the electron beam apparatus described above can use ahydrostatic bearing stage mechanism used in the atmosphere as it is, ahighly accurate X-Y stage equivalent to a highly accurate stage foratmosphere used in an exposure apparatus and so on can be implemented inan X-Y stage for an electron beam apparatus substantially at the samecost and in the same size.

[0210] The structure and positioning of the static pressure guides andactuators (linear motors) described above are merely embodiments in allsense, and any of static pressure guides and actuators can be applied ifit is usable in the atmosphere.

[0211]FIG. 22 shows exemplary values for the sizes of the annular member26-2 of the differential pumping mechanism, and the annular groove 27-2formed therein. In this example, the annular groove has a doublestructure comprised of 27 a-2 and 27 b-2 which are spaced apart in aradial direction.

[0212] A flow rate of the high pressure gas supplied to the hydrostaticbearings is generally at about 20 L/min (converted to the atmosphericpressure). Assuming that the working chamber 31 is evacuated by a drypump having an pumping speed of 20000 L/min through a vacuum pipe havingan inner diameter of 50 mm and a length of 2 m, the pressure in thechamber 31 is approximately 160 Pa (approximately 1.2 Torr). In thisevent, if the dimensions of the annular member 26-2 of the differentialpumping mechanism, annular groove and so on are determined as shown inFIG. 22, the pressure in the electron beam irradiation space 30-2 can beset at 10⁻⁴ Pa (10⁻⁶ Torr).

[0213]FIG. 23 illustrates a piping system for the apparatus illustratedin FIG. 22. The working chamber 31 defined is connected to a dry vacuumpump 53-2 through vacuum pipes 74-2, 75-2. Also, the annular grove 27-2of the differential pumping mechanism 25-2 is connected to a turbomolecular pump 51-2, which is an ultra-high vacuum pump, through avacuum pipe 70-2 connected to an evacuate port 28-2. Further, the insideof the column 71 is connected to a turbo molecular pump 52-2 through avacuum pipe 71-2 connected to the evacuate port 18-2. These turbomolecular pumps 51-2, 52-2 are connected to the dry vacuum pump 53-2through vacuum pipes 72-2, 73-2. (While in FIG. 23, a single dry vacuumpump is in double use for a roughing pump as the turbo molecular pumpand a vacuum evacuation pump for the vacuum chamber, it is contemplatedthat separate dry vacuum pumps may be used for evacuation depending onthe flow rate of the high pressure gas supplied to the hydrostaticbearings of the X-Y stage, the volume and inner surface area of thevacuum chamber, and the inner diameter and length of the vacuum pipe.)

[0214] The hydrostatic bearing of the X-Y stage are supplied with highlypure inert gas (N₂ gas, Ar gas or the like) through the flexible pipes21-2, 22-2. The gas molecules blown out from the hydrostatic bearingsdiffuse in the working chamber, and are exhausted by the dry vacuum pump53-2 through the evacuate ports 19-2, 20 a-2, 20 b-2. Also, the gasmolecules introducing into the differential pumping mechanism and theelectron beam irradiation space are sucked from the annular groove 27-2or the bottom of the column 71, evacuated by the turbo molecular pumps51-2 and 52-2 through the evacuate ports 28-2 and 18-2, and evacuated bythe dry vacuum pump 53-2 after they have been pumped by the turbomolecular pump. In this way, the highly pure inert gas supplied to thehydrostatic bearings is collected and evacuated by the dry vacuum pump.

[0215] On the other hand, the dry vacuum pump 53-2 has an evacuate portconnected to a compressor 54-2 through a pipe 76-2, while the compressor54-2 has an evacuate port connected to the flexible pipes 21-2, 22-2through pipes 77-2, 78-2, 79-2 and regulators 61-2, 62-2. Therefore, thehighly pure inert gas exhausted from the dry vacuum pipe 53-2 is againpressurized by the compressor 54-2, regulated to a proper pressure bythe regulators 61-2, 62-2, and again supplied to the hydrostaticbearings of the X-Y table.

[0216] As described above, the gas supplied to the hydrostatic bearingsmust be purified as high as possible to maximally exclude moisture andoil components, so that the turbo molecular pumps, dry pump andcompressor are required to have structures which prevent moisture andoil components from introducing into gas flow paths. It is alsoeffective to provide a cold trap, a filter or the like (60-2) in themiddle of the discharge side pipe 77-2 of the compressor to trapimpurities such as moisture and oil components mixed in a circulatinggas such that they are not supplied to the hydrostatic bearings.

[0217] In this way, since the highly pure inert gas can be circulatedfor reuse, the highly pure inert gas can be saved. In addition, sincethe inert gas is not supplied in an uncontrolled manner into a chamberin which the apparatus is installed, the possibility of accidents suchas suffocation by the inert gas can be eliminated.

[0218] The circulating pipe system is connected to a highly pure inertgas supply system 63-2 which serves to fill the highly pure inert gasinto the entire circulating system including the working chamber 31,vacuum pipes 70-2-75-2, and pressurizing pipes 1676-1680, and to supplythe shortage if the flow rate of the circulating gas is reduced by somecause.

[0219] It is also possible to use a single pump as the dry vacuum pump53-2 and the compressor 54-2 by providing the dry vacuum pump 53-2 witha function of compressing to the atmospheric pressure or higher.Further, the ultra-high vacuum pump for use in evacuating the column 72may be implemented by a pump such as an ion pump, a getter pump insteadof the turbo molecular pump. However, when such an entrapment vacuumpump is used, a circulating piping system cannot be built in thisportion. Also, a dry pump of another configuration such as a diaphragmdry pump may of course be used instead of the dry vacuum pump.

[0220] In the constitutions of the electron beam emitting tip and thepumping mechanisms for the space around the emitting tip as describedabove, the stage apparatus can be accurately positioned in the vacuumworking chamber. Further, it is possible to create high quality imagedata because the pressure around the emitting tip is hardly increased.These constitutions are applicable to embodiments of the electron beamapparatus which will be explained below, as well as the apparatus shownin FIG. 8.

[0221] Next, a variety of embodiments of the electron beam apparatusaccording to the present invention will be described other than theembodiment illustrated in FIG. 8.

[0222]FIG. 24 illustrates an embodiment of an electro-optical system 70which can be applied to the electron beam apparatus according to thepresent invention. In this embodiment, an electron gun is constructed tohave a plurality of emitters 1-3, 2-3, 3-3, i.e., multiple emitters foremitting multiple beams, and can conduct a desired test even if one ofthese emitters fails. An electron beam emitted from each emitter isconverged by condenser lenses 4-3, 6-3, and forms a cross-over in anaperture 9-3. Then, an image of the primary electron beams or multiplebeams, is focused on the surface of a wafer W through an objective lens8-3.

[0223] Secondary electron beams emitted from the wafer W areindividually converged by an acceleration electric field created by theobjective lens 8-3, and deflected by the ExB separator 10-3 to beseparated from the primary optical system. Then, the secondary electronbeams are enlarged by enlarging lenses 11-3, 12-3, pass through amulti-aperture plate 13-3 formed with apertures on the same circle, andare detected by detectors 14-3, 15-3, 16-3 to generate electric signals.The generated electric signals are processed in an image processing unit(not shown).

[0224] With reference to FIGS. 25 through 27, arrangements of emitterchips, i.e., electron beam emission sources 32-3 of the electron gunwill now be described.

[0225] In an example illustrated in FIG. 25, the emitter chips 32-3 arelinearly arranged in the Y direction to form a plurality of emitter chipgroups 33-3. The emitter chip groups 33-3 are positioned on the samecircle 31-3 centered at an optical axis C-3, and set such that when theyare projected to a line in the X direction (the direction in which theprimary electron beams are scanned on the wafer W) orthogonal to theoptical axis C-3, the projected images of the emitter chips are spacedsubstantially at equal intervals in the X direction. This positionalrelationship is similar to that described above with reference to FIG.9A. The emitter chips 32-3 in the emitter chip group 33-3 are connectedin parallel with power source, so that as one of the emitter chips isarbitrarily selected and only this chip is applied with a voltage, anelectron beam can be emitted from the selected emitter chip alone. Sincethe emitter chip groups 33-3 are spaced from one another as describedabove, electron beams emitted from emitter chips respectively selectedas described above from the emitter chip groups are spaced at equalintervals in the X direction. Therefore, by scanning these electronbeams in the X direction only in a spacing between irradiated spots ofthe electron beams on the surface of the wafer, the wafer is scannedover a width equal to (the spacing between spots)×(the number of emitterchips). Preferably, each of emitter chips is in the shape of cone,quadrangular pyramid, or the like.

[0226] In an example of FIG. 26, emitter chip groups 33-3 are comprisedof a plurality of emitter chips 32-3 positioned on the samecircumference 31-3, and similar to the case of FIG. 26, one arbitraryemitter chip in each emitter chip group can be applied with a voltage.Since the spacing between emitter chips applied with the voltagesslightly varies in the X direction depending on the selection of emitterchips, a scanning width must include a margin and be larger than thespacing between the spots described in connection with FIG. 25.

[0227] In another example illustrated in FIG. 27, each emitter chipgroup 33-3 is comprised of emitter chips which are arranged in 3×3matrix. By arranging them in a matrix, a large margin is not requiredfor the scanning width as compared with the arrangement of the emitterchips illustrated in FIG. 26, and the field curvature can be minimized.

[0228] In the electro-optical systems 70 described with reference toFIGS. 24 through 27, the electron gun comprises a plurality of groups ofemitter chips, and a voltage is applied to one emitter chip arbitrarilyselected from each emitter chip group to generate an electron beam.Therefore, even if any emitter chip fails, another emitter chip in thesame group can be used to emit an electron beam, and thus it is possibleto avoid a trouble due to a failure of an emitter chip.

[0229]FIG. 28 illustrates another embodiment of the electro-opticalsystem 70 utilized in the electron beam apparatus according to thepresent invention. In this embodiment, primary electron beams arecomprised of multiple beams, and the field curvature aberration, whichis the largest one of aberrations of the primary electron beams, can belimited. In this electro-optical system 70, a cathode 2-4 made of anLaB₆ single crystal which is processed to be multi-beam emitters, isplaced at the center of an electron gun 1-4. An electron beam emittedfrom the cathode is converged by a condenser lens 3-4 to form across-over. A first multi-aperture plate 4-4 is provided between thelens 3-4 and the cross-over, and is positioned such that aperturesthereof substantially match locations at which respective beams from thecathodes 2-4 are strong. The beams passing through the multi-apertureplate are demagnified by two stages of reducing lenses 5-4, 7-4, furtherdemagnified by an objective lens 10-4, and focused on a wafer W. In FIG.28, 6-4 and 8-4 indicate a first and a second reduced image.

[0230] Electron beams emitted from the wafer W are converged by anaccelerating electric field created by the objective lens 10-4,deflected by an ExB separator 9-4 to be separated from the primaryoptical system, enlarged by enlarging lenses 12-4, 13-4, and detected bydetectors 15-4 after passing through a second multi-aperture plate 14-4having apertures arranged on the same circle, thereby they are convertedto electric signals. The resulting electric signals are processed in animage processing unit (not shown).

[0231] The electron gun 1-4 comprises a LaB₆ single crystal cathode of athermal electron emission type. The shape of the cathode 2-4 at a bottomis illustrated in detail in FIG. 29 (front view) and FIG. 30 (sideview). The cathode is generally made of an LaB₆ single crystal in theshape of a 2 mmφ cylinder. As illustrated, the bottom is cut at an angle22-4 of 45°, and an annular protrusion 23-4 having a triangularcross-section is left along the peripheral edge of a bottom surface 24.Then, portions of the annular protrusion are cut off to form a pluralityof protrusions in the shape of quadrangular pyramid having an incline26-4 angled at 45°, i.e., emitter regions 25-4. These emitter regionsare set such that when they are projected to a line in the X direction(the direction in which the primary electron beams are scanned on thewafer W) orthogonal to the center line of the bottom surface 24-4 (thecenter line matches the optical axis of the primary electro-opticalsystem), the projected emitter regions are spaced substantially at equalintervals in the X direction. This positional relationship is similar tothat described above in connection with FIG. 9A. To prevent electronsfrom being emitted from regions between the respective emitter regionsand the bottom surface 24-4 inside the emitter regions, a sufficientdifference in height is taken between the bottoms of the emitter regionsand these portions.

[0232] The electron gun having the cathode structure illustrated inFIGS. 29 and 30 not only can be used as the electron gun for theelectro-optical system in the third embodiment illustrated in FIG. 28,but also can be used as the electron gun for the electro-optical systemin the first embodiment illustrated in FIG. 8. Further, it can be usedas an electron gun for other embodiments of the electro-optical system70 described below.

[0233] In the electro-optical system in the electron beam apparatusdescribed with reference to FIGS. 28 through 30, multiple beams can beproperly generated by a single electron gun. In addition, since thefield curvature can be substantially corrected, a large number of beamscan be generated with the same aberration, thereby making it possible tosignificantly improve the throughput of a testing apparatus.

[0234]FIGS. 31 through 33 are a plan view and side views (partiallycross-sectional views) illustrating another embodiment of an electrongun which can be applied to the electro-optical system 70 in theelectron beam apparatus according to the present invention. Thesedrawings illustrate, in enlarged view, the vicinities of a cathode and aWehnelt which constitute an electron beam emission region of theelectron gun. The electron gun of this embodiment can also be used as anelectron gun for any embodiment of the electron beam apparatus accordingto the present invention. The electron gun of this embodiment is capableof generating multiple beams with high performance, and moreover, thecathode of the electron gun can be readily aligned with a controlelectrode.

[0235] As illustrated in FIGS. 31 and 32, an electron gun 1-5 of thisembodiment comprises a cylindrical cathode body 2-5, and a controlelectrode, i.e., a Wehnelt 5-5 arranged to surround a bottom of thecathode body 2-5. The columnar cathode 2-5 has, at the bottom thereof, aplurality of (six in this embodiment) emitters 3-5 which form electronbeam emission regions. These emitters 3-5 have sharp peaks 4-5 formed bymachining the bottom of the cathode 2-5 into tapered shapes (pyramidalshapes), and emit electron beams from the bottoms. The position of theemitter 3-5 on the bottom of the cathode is previously determined suchthat the distance Lx between mutually adjacent ones of the positionswhich are formed by projecting the peaks 4-5 of the respective emitterson the X-axis, is constant. This relationship is similar to thatdescribed above with reference to FIG. 9A. Also, the peaks of all theemitters 3-5 are formed to be present on the same plane P1-P1, asillustrated in FIG. 32. Although the two-dimensional interbeamdistances, i.e., the two-dimensional distance between the peaks of theemitters 3-5 cannot be made equal to one another, distances dl and d2 inthe circumferential direction between the peak of an emitter 3 a-5 andpeaks of adjacent emitters 3 b-5 and 3 f-5 can be made equal to eachother by optimally selecting an angle θ formed by a line which connectsthe bottom of the emitter 3 a-5 with an axial line 0-0 of the cathode2-5, which defines the optical axis of the electron gun 1-5, and theX-axis, as illustrated in FIG. 31. The control electrode, i.e., theWehnelt electrode 5-5 has a cylindrical end closed by an end wall 6-5,as is apparent from FIG. 32. The end wall 6-5 has through holes orapertures 7-5 positioned correspondingly to the respective emitters 3.The Wehnelt electrode may have a single aperture of such dimensions thatsurround all the emitters.

[0236] The number of electron beam emission regions, i.e., emittersformed at the bottom of the cathode may be an arbitrary plural numberequal to or larger than two. The shape of the emitter is not limited tothe pyramidal shape illustrated in FIGS. 31 and 32, but may be in anarbitrary shape such as a cone, by way of example, as long as such ashape can emit electron beams from its bottom. The cathode and Wehneltmay be formed of the same materials as those in a conventional electrongun. Further, the size of the openings 7 formed through the Wehnelt canbe determined as appropriate.

[0237] The throughholes 7-5 need to be correctly positioned with respectto the emitters 3-5. The positioning is performed by an alignmentmechanism illustrated in FIG. 33. In FIG. 33, the Wehnelt electrode 5-5is attached to a bottom of a cylindrical supporting base 8-5. A baseplate 11-5, which forms a part of the alignment mechanism, is disposedin the supporting base 8-5. The base plate 11-5 is made of an insulatingmaterial, and carried on a plurality (in this embodiment, a total offour, two each on the X and Y-axis lines, though only two on the X-axisare shown in the drawing) of adjustable screws 12 a-5, 12 b-5 screwedinto a bottom plate 9-5 of the supporting base 8-5. Between the baseplate 11-5 and a spring receptacle 15-5 fixed on the supporting base8-5, a spring (a leaf spring in this embodiment) 14-5 is interposed, sothat the base plate 11-5 is normally urged by this spring toward theadjustable screws 12 a-5, 12 b-5. Preferably, the spring and springreceptacle are arranged at positions corresponding to the adjustablescrews 12 a-5, 12 b-5. On the supporting base 8-5, a plurality (in thisembodiment, a total of four, two each on the X and Y-axis lines, thoughonly two on the X-axis are shown in the drawing) of adjustable screws 13a 5-8 b-5 are screwed into the supporting base 8-5. The adjustablescrews 12 a-5, 12 b-5 can adjust the position of the base plate 11-5 inthe vertical direction, while the adjustable screws 13 a-5, 13 b-5 canadjust the position of the base plate 11-5 in the X and Y directions.The cathode 2-5 is fixed over the base plate 11-5 through a plurality ofmounting members 17-5. 18-5 designates a heating pyrolic graphite forheating the cathode.

[0238] While in this embodiment, a leaf spring is employed as thespring, a coil spring or another arbitrary elastically deformableelastic material may be used.

[0239] In the alignment mechanism illustrated in FIG. 33, the Wehneltand cathode have been previously machined such that all the emitters 3-5are simultaneously aligned with all the through holes or apertures 7-5of the Wehnelt electrode 5-5, by matching a rotating direction (arotating direction about the axial line 0-0 in FIG. 33), X direction (inthe left-to-right direction on the sheet surface in FIG. 33), Ydirection (in the direction vertical to the sheet surface in FIG. 33),and inclination of the cathode 2-5 with respect to the Wehnelt electrode5-5. Considering the alignment in the rotating direction, errors can belimited within a range determined by the accuracy during machining, ifthe alignment mechanism is manufactured to prevent relative rotation ofthe cathode 2-5 to the Wehnelt electrode 5-5.

[0240] An adjustment in the X direction is made using a pair of theadjustable screws 12 a-5 and 12 b-5 arranged on the X-axis, and anadjustment in the Y direction is made using a pair of adjustable screws(not shown) positioned on the Y-axis (in FIG. 33, an axial line whichintersects the axial line 0-0 and is orthogonal to the sheet surface).When the inclination of the plane P1-P1 (FIG. 32) with the plane onwhich the apertures exist (here, the plane on which the top surface ofthe end wall is positioned), i.e., a plane P2-P2 (FIG. 32) is wrong, thedistance between the cathode and the Wehnelt in the Z direction (thedirection vertical to the sheet surface in FIG. 33) is changed, so thatthe inclination is adjusted by the adjustable screws 12 a-5, 12 b-5, andtwo adjustable screws not shown (or two adjustable screws arranged inthe direction vertical to the sheet surface).

[0241] According to the electron gun as described above, the relativeposition of each of the multiple emitters to the each of the aperturesof the Wehnelt can be made identical to that of a single beam.Therefore, the intensity of each of the multiple beams can be madesubstantially similar to that of the single beam.

[0242]FIGS. 34 through 38 are diagrams for explaining furtherembodiments of the electron gun which can be employed in theelectro-optical system 70 in the electron beam apparatus according tothe present invention. Likewise, the electron gun of this embodiment isapplicable as the electron gun for embodiments of the electro-opticalsystem described below, other than the aforementioned embodiments of theelectro-optical system 70. The electron gun of this embodiment iscapable of emitting multiple beams having a relatively large beamcurrent with small temporal fluctuations.

[0243]FIGS. 34A and 35 illustrate a plan view and a side view of abottom of a cathode 1-6 for use in the electron gun. The cathode 1-6 isformed by machining an LaB₆ column 10-6 having an end surface defined bya (100) surface of a single crystal LaB₆ and an outer diameter d1. Theend surface of this column is mirror polished, and two surfacesperpendicular to the end surface and held by carbon are also polishedinto parallel plain surfaces. When the LaB₆ column 10-6 is machined toform the cathode, a jig borer is used. A tool a-6 made of a grindingstone having the structure shown in FIG. 36 is mounted on the jig borerin place of a drill, and using this tool a-6, the LaB₆ column 10-6 iscut to and shaped to form a predetermined number (six in thisembodiment) of conical protrusions, i.e., emitters 12-6 are formed on acircle 15-6 centered at an optical axis. Bottoms 13-6 of the emitters12-6 form emission regions which can emit strong electron beams, asillustrated in FIG. 34B. As can be seen from the structure of the toola-6 illustrated in FIG. 36 and described later, extremely small plainsurfaces (10-50 μmφ) comprised of polished end surfaces of the cylinderare left on the bottom 13-6, without cutting by the tool, and electronbeams are emitted from these plain surfaces. The number of the emitters12-6 is six so that six electron beams can be generated in thisembodiment, and the positions of the emitters 12-6 are determined suchthat spacing distances Lx between adjacent ones of the positions formedby projecting the centers of the respective emitters 12-6, i.e., thebottoms 13-6 onto the X-axis are all equal to one another. This issimilar to that described in connection with FIG. 9A. The positions ofthe emitters can be correctly determined as limited by the accuracy ofthe jig borer. By optimizing the angle θ formed by the X-axis and a linepassing the bottom 13-6 of one emitter 12-6 a and the axial line 0-0 ofthe cathode (FIG. 35), the ratio of a maximum value L1 to the best valueL2 of the spacing distance between electron beams is approximated to1.0. This can be optimized by varying the diameter of the circlecentered at the optical axis, and creating a design drawing with thevalue of the spacing Lx being fixed.

[0244] The tool a-6 illustrated in FIG. 36 comprises a mounting portiond-6 of a small diameter, for mounting on the jig borer, on one end side(on the lower side in FIG. 36B) of a columnar grinding stone; and aconical hole c-6 in an end surface d-6 on the other end side. Theconical surface having the end surface b-6 and the conical surfaceconstitutes a cutting surface to be used to cut the end surface of theLaB₆ column 10-6. The tool a-6 is further formed with an axial hole e-6which extends from the bottom of the conical hole c-6 in the axialdirection of the tool. This hole is provided for confirming throughlight whether a conical protrusion constituting an emitter is formed ata correct position. In addition, a coolant and an abrasive material maybe introduced from this hole. When cut with this tool a-6, small groundplain surfaces are left on the leading surface of the cone, withoutbeing cut, due to the existence of the axial hole, as described above.Alternatively, in place of the grinding stone, a cutting tool havingdiamond grains embedded in a metal may be used.

[0245]FIGS. 37 and 38 illustrate the structure which is a combination ofthe cathode 1-6 and Wehnelt 2-6 illustrated in FIGS. 34 and 35. TheWehnelt 2-6 comprises a cylinder section 21-6 surrounding thecircumference of the cathode 1-6, and an end wall 22-6 surrounding theend surface. The end wall 22-6 is formed with a plurality (six in thisembodiment) of throughholes or apertures 23-6 aligned to the positionsof the bottoms 13-6 of the emitters on the cathode. Since theequi-potential surface near the throughholes 23-6 of the Wehnelt 2-6 isrecessed toward the emitters at the positions of the holes 23-6, asindicated by a dotted line Ev, electron beams emitted from the emittersare drawn out. Since the end portion of the cathode 1-6 (except for thebottom regions of the emitters) is surrounded by the end wall 22-6 ofthe Wehnelt 2-6, even if an uncut portion 16-6 exists on the end surfaceof the cylinder 10-6, no throughhole is formed in the end wall of theWehnelt corresponding to that position, so that no electron beam will beemitted to the outside. Therefore, the shape of the cathode at aposition except for those facing the holes 23-6 may be anyhow.

[0246] In essence, it is only required that the LaB₆ conical isaccurately left as the emitter and the aforementioned extremely smallground plain surfaces (10-50 μmφ) are left on the bottoms of theemitter. Also, cut traces may be left on the inclines of conicalemitters. Furthermore, the areas of the plain surfaces at the bottoms ofthe respective emitters may vary as long as the total area of all (sixin this embodiment) the plain surfaces is equal to or less than 100 μm².

[0247] While the foregoing embodiment of the electron gun has beendescribed for the emitter the shape of which is conical, the shape ofthe emitter is not limited to be conical, but may be pyramidal (forexample, in the shape of quadrangular pyramid).

[0248] In the electron gun described above, since a fine grinding stoneis used for grinding and machining, a rigid and fragile crystallinematerial such as LaB₆ can be machined. Also, since the positionalaccuracy of the emitters is determined by the accuracy of the jig borer,an accuracy of approximately 50 μm can be achieved. Also, since theplain surfaces at the bottoms of the emitters are machined only in theinitial mirror polishing, the positions in the optical axis and thesurface roughness are held in a high accuracy. Moreover, since thecathode portions other than those facing the throughholes of the Wehneltmay have any shape, the cathode is easy to manufacture.

[0249]FIGS. 39 through 42 illustrate other embodiments of an electrongun which is applicable to the electro-optical system 70 comprised inthe present invention. Likewise, the electron gun of this embodiment canbe used as an electron gun for any electro-optical system 70 in theelectron beam apparatus according to the present invention. Also, thisembodiment of the electron gun facilitates the manufacturing of acathode for emitting multiple beams, and is capable of emittingmulti-beams without variations in intensity.

[0250]FIG. 39 illustrates the shape of a bottom of a cathode in theelectron gun of this embodiment, wherein FIG. 39A is a top plan view,FIG. 39B is a cross-sectional view taken along a line B-B in FIG. 39A,and FIG. 39C is a cross-sectional view taken along a line C-C in FIG.39A. A method of manufacturing the cathode illustrated in FIG. 39 willbe described. First, a Ta (tantalum) single crystal with an end surfacehaving a crystal orientation <310> is used, and one surface thereof ismirror polished to form a mirror surface 2-7 (FIGS. 39B and 39C). Then,two surfaces 1-7 (FIG. 40) exhibiting a good orthogonality to the mirrorsurface 2-7 are formed, and heated as sandwiched by graphite.Subsequently, both sides of the mirror surface 2-7 are cut at an angleof approximately 45° while leaving a circumference having a width of 10μm in the radial direction at a position of the mirror surface 2-7 atwhich a protrusion is formed for the cathode. In this manner, asillustrated in FIG. 39B, a ridge-shaped solid is formed having a mirrorsurface circumference with a radial width of 10 μm, and two opposinginclines 3-7 with a relative angle, i.e., an apical angle ofapproximately 90°.

[0251] Next, orthogonal X-axis and Y-axis are determined, and directionsX′ and Y′ forming an angle φ to these two axes are determined. TheX-axis indicates a direction in which the electron beams are scanned,and the Y-axis indicates the direction orthogonal to that. φ is, forexample, 5°. Then, four points P1-P4, crossing in the X′ and Y′directions are marked on the circumference of the ridge-shaped solid,and another four points P5-P8 are marked. In this event, the value ofthe angle φ is determined and points P5-P8 are positioned such that theeight points P1-P8, when projected onto the X-axis, are spaced at equalintervals (similar to the arrangement illustrated in FIG. 9A). Then,eight quadrangular truncated conical protrusions having the points P1-P8as peaks, and substantially rectangular bases are formed by cutting theridge-shaped solid (FIG. 39A). The protrusions formed in this event isas shown in FIG. 39C, wherein a top surface has a width of 50 μm in theazimuth direction (circumferential direction), and two inclines 4-7formed by the new cutting have an angle of approximately 45° to themirror surface 2-7, therefore, the relative angle, i.e, an apical angleof the two inclines is set to approximately 90°.

[0252] In the foregoing manner, eight quadrangular truncated conicalprotrusions each with a top surface having a rectangular shape of 10μm×50 μm, which, when projected onto the X-axis, are spaced at equalintervals, are formed as illustrated in FIG. 40.

[0253] Since a Ta single crystal is available at a relatively low costand readily machined, the cathode can be readily manufactured. Thoughits work function is relatively high, i.e., 4.1 eV, it can be used ifthe cathode temperature is increased.

[0254]FIG. 41 illustrates a main portion of an electron gun whichcomprises such a cathode as illustrated in FIGS. 39 and 40, wherein 24-7designates graphite; 25-7 a supporting electrode; and 26-7 a Wehneltelectrode. The cathode is sandwiched by the graphite 24-7, and supportedby the supporting electrode 25-7. The Wehnelt electrode 26-7 whichcovers the entire surface of the cathode is formed with eightthroughholes 26 a-7-26 h-7 corresponding to the protrusions on thecathode, and the center of each throughhole is aligned to the center ofa corresponding protrusion by adjusting the supporting electrode 25-7 inthe X and Y directions.

[0255] Further, the parallelism of the surface of the Wehnelt electrode26-7 to a plane which connects the bottoms of the cathode requires anaccuracy. In other word, the distances between the surfaces of the holesof the Wehnelt electrode 26-7 and the cathode in the optical axisdirection must be substantially identical for all of the eightprotrusions. Therefore, the supporting electrode 25-7 is provided with adevice (not shown) for adjusting the inclination of the cathode. Also,for matching absolute values of the distances in the optical axisdirection, a device (not shown) is provided for moving the Wehneltelectrode 26-7 in the optical axis direction.

[0256]FIG. 42 is a diagram for explaining a further embodiment of theelectron gun which can be applied to the electro-optical system 70 inthe electron beam apparatus according to the present invention.Likewise, the electron gun of this embodiment can be used as an electrongun for any electro-optical system 70 in the electron beam apparatusaccording to the present invention. Also, this embodiment facilitatesthe manufacturing of a cathode for emitting multiple beams, and iscapable of emitting multi-beams without variations in intensity. FIG. 42illustrates only the cathode of the electron gun in this embodiment.FIG. 42A is a plan view of the cathode, and FIG. 42B is across-sectional view taken along a line B-B in FIG. 42A. In FIG. 42A,21-7 designates a column of single crystal Hf (hafnium). The providedcolumn has a crystal orientation of <100> on the end surface, and thesurface is machined to leave eight protrusions 22-7 on a circumferenceof 4 mm diameter, as is the case with FIG. 39. However, in this event,each protrusion 22-7 has a plain portion of approximately 30 μm diameterleft on its peak, as illustrated in FIG. 42B, and is in the shape ofcircular truncated cone having an apical angle of approximately 90°. Theplain portion has an end mirror polished before the protrusions aremachined, thereby holding the eight plain portions substantially in thesame plain shape. Since Hf has a low work function of 3.4 eV, electronscan be emitted at a temperature lower than Ta.

[0257] The cathode having the structure illustrated in FIG. 42 isincorporated in the electron gun illustrated in FIG. 41, and thesupporting electrode 25-7 is adjusted in the X and Y directions to alignthe center of each protrusion to the center of a corresponding hole.Also, as described in connection with FIG. 41, the inclination of thecathode is adjusted by the supporting electrode 25-7, and the Wehnelt26-7 is moved in the optical axis direction for adjustment to match theabsolute values of the distances in the optical axis direction.

[0258] In the two embodiments of the electron guns described withreference to FIGS. 39 through 42, the cathode is provided with eightprotrusions so that eight electron beams can be emitted. However, itgoes without saying that an arbitrary number of protrusions can beprovided, not limited to eight. Also, the size of the plain surface atthe bottom of the protrusion is not limited to the example describedabove, and may be set to an appropriate size. However, it is preferableto set the diameter to 50 μm or less, or the width in the radialdirection to 10 μm or less, and the width in the azimuth direction to100 μm or less.

[0259] In the electron gun described above, when the cathode foremitting multiple beams is formed of single crystal Ta, whichfacilitates the machining, the cathode is readily manufactured. When thecathode is formed of single crystal Hf, the work function of the cathodecan be reduced. Since a single crystal is used, no variations are foundin material, so that there is few variations in the intensities ofmultiple beams.

[0260] The materials for the cathode for emitting multiple beams, andthe shape of the bottom, so far described, can be applied to a cathodefor emitting a single beam.

[0261]FIG. 43 illustrates another embodiment of the electro-opticalsystem 70 incorporated in the electron beam apparatus according to thepresent invention, together with a CPU 15-8 which is a control unittherefor. In this embodiment, a Zr-W thermal field emission cathode 2-8is disposed in a Schottky shield 1 a-8 of an electron gun 1-8. Thiscathode 2-8 has a bottom slightly projected from the Schottky shield 1a-8 to emit an electron beam parallel with the optical axis from thebottom. In the present invention, the cathode 2-8 is projected moredownward from the Schottky shield 1 a-8 to facilitate the emission ofelectron beams from four surfaces of <100> in an upper portion of thecathode.

[0262] The electron beams emitted from the four surfaces in the upperportion of the cathode characteristically is larger (stronger) inluminance than the electron beam emitted from the bottom of the cathodebecause the surfaces are close to a heating portion. The five electronbeams emitted from the four surfaces in the upper portion of the cathodeand from the bottom of the cathode are converged by a condenser lens 3-8to image cross-over on an aperture 5 a-8 on an aperture plate 5-8. Afirst multi-aperture plate 4-8 is placed adjacent to and below thecondenser lens 3-8. As illustrated in FIG. 44, the first multi-apertureplate 4-8 has small apertures 4 a-8 of 5 μmφ at locations quadrisectinga circumference centered at the optical axis. The small apertures 4 a-8transfer therethrough the four strong electron beams emitted from thefour surfaces in the upper portion of the cathode. The firstmulti-opening plate 4-8 intercepts the electron beam which travels onthe optical axis.

[0263] As illustrated in FIG. 44, the four small apertures 4 a-8 on thefirst multi-aperture plate 4-8 is set such that distances D between theadjacent small apertures 4 a-8 are equal, and when projected in the Xdirection, three distances Lx between the adjacent small apertures 4 a-8are equal (similar to that in FIG. 9A). The electron beams which havepassed the four small apertures 4 a-8 are reduced by a reducing lens 6-8and an objective lens 8-8. In this manner, when a reduction ratio is1/50, for example, electron beams of 100 nmφ are produced on the surfaceof a wafer W. When electron beams are spaced at intervals of 100 μm onthe surface of the wafer, the distance Lx between the small apertures 4a-8 on the opening plate 4-8 projected in the X direction may be changedto 5 mm.

[0264] This reduction ratio of 1/50 can be largely varied by slightlychanging the excitation of the reducing lens 6-8 and objective lens 8-8.Secondary electrons generated by the irradiation of the primary electronbeams are accelerated by the objective lens 8-8, and enlarged by theenlarging lenses 10-8 and 11-8 and focused on small apertures on asecond multi-aperture plate 12-8 for detection.

[0265] The secondary electrons traveling near the second multi-apertureplate 12-8 substantially fully pass the small aperture by a convex lensaction which is produced by a high voltage applied to a detectors 13-8and leaking from the small holes, and are detected by the four detectors13-8 and processed into an image by an image forming unit 14-8. Bycomparing images of corresponding locations of different chips, defectsand the like can be detected.

[0266] In the electron beam apparatus illustrated in FIG. 43, in orderto prevent the secondary electrons generated by the irradiation of thefour primary electrons from cross-talking, the distance D between theadjacent primary electron beams (FIG. 44) may be taken larger than thesum (P+Q) of a blurred beam P converted into a position on the wafer ofa secondary optical system and extension Q of back scattered electronsof the primary electron beams. Since the sum (P+Q) varies depending onthe energy of the primary electron beams, a large spacing D must betaken between the primary electron beams for entering high energyprimary electron beams. For this purpose, the excitation of the reducinglens 6-8 may be adjusted in a direction in which the focal distancebecomes longer, by an instruction of the CPU 15-8, to adjust thereduction ratio to approach one. These adjusting parameters are storedin a memory associated with the CPU 15-8, and fetched and used asrequired for instructions.

[0267] The prevention of cross-talk by adjusting the reducing lens canbe applied to electro-optical systems in the electron beam apparatus inother embodiments disclosed in the present specifications and theirexemplary modifications, not limited to the electron beam apparatusillustrated in FIG. 43.

[0268]FIGS. 45 and 46 are diagrams for explaining the principles ofproviding information at a location deeper than a surface 23-8 of thewafer W, when image information of the wafer is acquired using theelectron beam apparatus according to the present invention. Asillustrated in a right-hand region of FIG. 45, when a primary electronbeam 24-8 scans a location beneath the surface 23-8 of the wafer W atwhich a pattern 25-8 of a different material such as tungsten exists,secondary electrons 27-8 are emitted from an incident point on thesurface 23-8, and secondary electrons 26-8 are generated when reflectedelectrons 27-8 of back scattered primary electrons by the pattern 25-8exit from the surface of the wafer. As illustrated in a left-hand regionof FIG. 45, when primary electrons 21-8 scan a location beneath thesurface 23-8 at which no pattern exists, secondary electrons 22-8 areemitted from the surface 23-8.

[0269]FIG. 46 is a graph showing the amount of generated secondaryelectrons on the vertical axis, with the horizontal axis representingthe energy of the primary electrons. The secondary electrons 22-8 or27-8 exhibit an intensity distribution which has a peak value in aleft-hand portion of the graph in FIG. 46, while the secondary electrons26-8 exhibit an intensity distribution which has a peak value in aright-hand portion. Therefore, when the secondary electrons 22-8, 27-8are removed as offsets, the secondary electrons 26-8, i.e., informationon layers beneath the surface of the wafer W can only be acquired.

[0270] Since the secondary electrons 26-8 emitted from a deep locationof the wafer are not generated unless the primary electron beam has acertain level of energy, the energy of the primary electron beam must beincreased to approximately 100 kV or higher. The energy of approximately100 kV is such that the energy still remains when the primary electronbeam returns after it has been reflected by a pattern deep beneath thewafer. For acquiring pattern information at a location not deep, theenergy of the primary electron beam may be lower. Also, for evaluatingthe surface of the wafer, approximately 0.5 keV is suitable. In otherwords, the energy of the primary electrons may be changed as appropriatein a range of 0.5 keV to 100 keV depending on the depth from thesurface.

[0271] The electron beam apparatus described with reference to FIGS. 43through 46 can realize a high throughput, and set the energy of theprimary electron beams in accordance with particular purposes, so thatdamages on a sample or a wafer can be minimized.

[0272] In a multi-beam based electro-optical system of a conventionalelectron beam apparatus, multiple beams are incident from an obliquedirection to a wafer W, so that a beam spot generated by each beamresults in the shape of ellipse which is longer in the beam incidentdirection, i.e., in a direction in which the beam is projected onto thewafer, thereby giving rise to a problem that a longitudinal resolutionis degraded. Also, in an electron beam apparatus which continuouslymoves a stage, variations in speed are inevitable even if the stage ismoved at a constant speed. Since variations in the speed of the stageresult in a failure in acquiring pixel data appropriately correspondingto positions on the surface of the wafer, no appropriate evaluations canbe achieved. Further, the stage normally includes parts made of metalsand the like, and as such a stage is moved, eddy currents are generatedin the metal parts by interactions with a magnetic field created by adeflector of the electro-optical system. Since the eddy currentsgenerate magnetic fields, a problem arises in that such magnetic fieldschange a direction in which electron beams are deflected.

[0273]FIG. 47 illustrates an embodiment of the electron beam apparatusaccording to the present invention which can solve the just beforementioned problems of the prior art example. This embodiment adds alaser mirror 20-9, a laser interferometer system 21-9, a deflectionamount correcting circuit 22-9, and a secondary electron deflector 23-9to the electro-optical system 70 in the electron beam apparatusillustrated in FIG. 8, and removes the enlarging lens 742 in thesecondary optical system. Therefore, description on components andoperations identical to those of the electron beam apparatus in FIG. 8is omitted, and operations related to the newly added components will bedescribed.

[0274] In FIG. 47, as a Y-table of a stage apparatus 50, on which awafer W is carried, is continuously moved in the Y direction, the movingspeed and current position are detected by the laser mirror 20-9 and thelaser interferometer 21-9. While a majority of the stage apparatus 50 isformed of insulating materials such as ceramics, metal materials areused for metal parts such as bearings and coatings on surfaces.

[0275] On the other hand, an ExB deflector 725 including anelectromagnetic deflector generates a relatively large static magneticfield. Since this static magnetic field extends over the stage apparatus50, an eddy current is generated when the Y-table is moved at a highspeed. Then, a magnetic field is generated by the eddy current, and as aresult, primary electron beams and secondary electron beams areundesirably deflected. If the primary electron beams are undesirablydeflected, the primary electron beams are irradiated to a locationdeviated from an intended location. On the other hand, if the secondaryelectron beams are undesirably deflected, the secondary electron beamscannot be efficiently passed through small apertures of a secondmulti-aperture plate 743 or are introduced into adjacent openings.

[0276] For correcting the deflection of the primary electron beams andsecondary electron beams due to the magnetic field generated by the eddycurrent, the relationship between the stage moving speed and therespective amounts of deflection for the primary electron beams andsecondary electron beams has been previously measured through a test inactual use, and the relationship between them has been previously storedin a corrective deflection amount table in the deflection amountcorrecting circuit 22-9. The deflection amount correcting circuit 22-9is provided as a part of a control unit 2 (FIG. 1), and searches thecorrective deflection amount table for the amounts of deflection to becorrected for the primary electron beams and secondary electron beamsbased on the moving speed of the Y-table measured by the laserinterferometer 21-9, and controls the electrostatic deflectors 725 and23-9 corresponding thereto to correct the amounts of deflection for theprimary electron beams and secondary electron beams. In this manner,since the primary electron beams and secondary electron beams areprovided with essential amounts of deflection, they can reach positionsintended thereby for irradiation and detection.

[0277] Also, when the deflection amount correcting circuit 22-9 detectsvariations in the stage speed while the Y-table of the stage apparatus50 is being moved to create image data, the circuit converts that intopositional fluctuations and corrects the positional fluctuations. Thepositional fluctuations are calculated by integrating the variations inspeed over time. Also, the positional fluctuations are corrected byinverting the sign of a voltage calculated by dividing the amount ofpositional fluctuations by a deflection sensitivity and supplying theinverted voltage to electrostatic deflectors (in the ExB deflector 725,and deflector 727) in the primary optical system and the electrostaticdeflector 23-9.

[0278] Since the electrostatic deflector for correcting the amount ofdeflection for the primary electron beams is positioned behind thereducing lens 724, a light path to the reducing lens 724 will not bechanged even if the amount of deflection is changed, so that theintensity of the primary electron beams will not be changed by thecorrection. Similarly, since the electrostatic deflector 23-9 forcorrecting the amount of deflection for the secondary electron beams ispositioned behind an enlarging lens 741 in the secondary optical system,blurred secondary electron beams will not be exacerbated even if thecorrection is made.

[0279] The electron beam apparatus illustrated in FIG. 47 can correctundesired deflection for the first and second electron beams caused bythe eddy current associated with the movement of the stage, andtherefore acquire image data corresponding to appropriate positions of asample. Also, a correction can be made even if the stage speed varies.Further, the generation of cross-talk can be reduced, even if multiplebeams are used, by setting the distance between the adjacent primaryelectron beams irradiated onto a sample to be larger than the resolutionof the secondary optical system.

[0280]FIG. 48 illustrates another embodiment of the electron beamapparatus according to the present invention. This embodiment adds adevice for adjusting a beam diameter using a standard mark 49-10 to theelectro-optical system 70 illustrated in FIG. 8. Therefore, detaileddescription on components and operations identical to those of theelectron beam apparatus in FIG. 8 is omitted.

[0281] Specifically, the conventional electron beam apparatus isdisadvantageous in requirements of a long time for a test due to anexcessively small pixel size depending on objects under testing, and afailure in providing a sufficient resolution due to an excessively largepixel size, on the contrary, since the pixel dimension is not changedeven if a fine pattern is tested, a coarse pattern is tested, or apattern dimension of an object under testing varies. Further, forenlarging a beam diameter, the conventional electron beam apparatusintentionally blurs a beam to enlarge the beam diameter, withoututilizing at all the advantage that a beam current is increased as thebeam diameter is enlarged, so that the conventional electron beamapparatus is disadvantageous in that the SIN ratio is largely lost whenthe beam diameter is enlarged. The electron beam apparatus illustratedin FIG. 48 can solve these problems.

[0282] In the electron beam apparatus illustrated in FIG. 48, a signaldetected in a detector 761 is processed in an image processing unit 763,and stored in an image storage device 43-10 under control of a CPU 41-10in a control unit 2 (FIG. 1). Then, the detected signal is displayed ona monitor 45-10, and compared with a standard pattern or image data ofthe same die on a different wafer to perform evaluations such asdetection of defects.

[0283] As previously described in connection with the electro-opticalsystem 70 in the electron beam apparatus illustrated in FIG. 8, whenprimary electron beams passing through the respective apertures of thefirst multi-aperture plate 723 are focused on the surface of a wafer W,and secondary electron beams emitted from the wafer are focused on thedetectors 761, it is necessary to pay particular attention to minimizethe influence of distortion and field curvature produced in the primaryoptical system and secondary optical system. Also, as described above,in regard to the relationship between the distances between the adjacentprimary electron beams and the secondary optical system, cross-talkbetween a plurality of beams can be eliminated by spacing the primaryelectron beams by a distance larger than the aberration of the secondaryoptical system.

[0284]FIG. 49 illustrates layouts of standard marks 49-10 of a pluralityof pattern sizes mounted on the stage apparatus 50. In the FIG., 49-10 ashows an L&S pattern (line and space pattern) of 0.05 μm, while 49-10 bshows an L&S pattern of 0.1 μm. In this manner, several kinds ofstandard marks corresponding to line widths of patterns under evaluationhave been provided on an X-Y stage. FIG. 49 shows only two kinds ofrepresentative standard marks.

[0285] Before conducting a test or the like, the X-Y stage of the stageapparatus 50 is moved to select a standard mark 49-10 which matches thesize of a pattern under detection on a wafer W and aligns the selectedstandard mark to the optical axis of the primary optical system, and thebeam diameter is changed in the following approach to select an optimalbeam diameter or a beam current suitable for the dimension of thepattern under detection.

[0286] In other words, the beam diameter can be changed by changing thebrightness of a beam from an electron gun by changing a bias voltageapplied to a Wehnelt of an electron gun 721. As a smaller bias isapplied to the Wehnelt, a current of the electron gun is increased toenhance the brightness, resulting in a larger current of the multiplebeams. As the beam current of the multiple beams is increased, the beamdiameter becomes larger due to a space charge effect.

[0287] Also, as another method of changing the beam diameter, a reducinglens 724 and an objective lens 726 are acted as a zoom lens to changethe beam dimension. In this case, since the reduction ratio is alsoadjusted in a direction in which it approaches one to increase the beamcurrent, the beam diameter becomes larger as well. However, in thiscase, the spacing between beams in the multiple beams also changes inthe same proportion, the method of changing the bias applied to theWehnelt may be employed if the spacing between the beams is not to bechanged.

[0288]FIG. 50 shows waveforms of signals detected by a detector which isobserved by the monitor 45-10 when the standard marks 49-10 a, 45-10 bare scanned by the multiple beams. FIGS. 50a-1-50 a-3 show signals whenthe standard mark 49-10 a is scanned with a variously changed beamdimension, and FIGS. 50b-1-50 b-3 show signals when the standard mark49-10 b is scanned with a variously changed beam dimension.

[0289]FIGS. 50a-1 shows a signal when the beam diameter is enlarged morethan the line width, in which case a beam having a dimension larger thanthe line width is used for scanning, in spite of a large beam current,so that the contrast S of the signal is not so large, and noise Nexhibits a large value due to the large beam current. The SIN ratio isapproximately 3.4.

[0290]FIGS. 50a-3 shows a signal when the beam diameter is extremelysmall, in which case although a faithful waveform (near a square wave)is generated, the contrast S of the signal is not large due to the smallbeam current. Also, the noise N is small corresponding to the beamcurrent which is small, and the S/N ratio is approximately 6.25.

[0291]FIGS. 50a-2 shows a signal when the beam diameter is suitable, inwhich case a blurred beam exhibits an adequate value, the beam currentis relatively large, the signal has large contrast S, and the S/N ratiois approximately 12.3.

[0292] Whether to select FIG. 50a-2 or 50 a-3 may be based on which hasa larger (contrast/noise) ratio. In the illustrated example, the beamdiameter which results in the pattern shown in FIG. 50a-2 may beselected for the mark 49-10 a.

[0293] For the mark 49-10 b, a similar calibration is made to select abeam dimension or a beam diameter suitable to this line width. In theshown example, the beam diameter which results in the pattern of FIG.50b-2 may be selected.

[0294] In this manner, a beam diameter or a beam current may be selectedin accordance with a pattern dimension under estimation such that theSIN ratio of a secondary electron signal detected by the detector ismaximized. More specifically, regular standard patterns having differentpitches are placed on the X-Y stage. A device is provided for storingsignal waveforms generated when the regular standard patterns arescanned. A device for calculating the amplitudes (S) of the signals fromthe signal waveforms, a device for calculating the amplitude (N) ofnoise, and a device for calculating the SIN ratio are provided. A pluralkinds of beam diameters are set, and a regular pattern having a pitchtwice the thinnest line width of a pattern under evaluation is scannedby these beam diameters, and the SIN ratios are calculated to select thebeam diameter which exhibits the highest SIN ratio, thereby making itpossible to evaluate a high SIN ratio for all patterns under evaluation.

[0295] Alternatively, as the regular standard patterns, standardpatterns may be found on a wafer under testing for use, instead of thoseon the X-Y stage, to examine the (signal/noise) ratio for the foundpatterns in a similar manner. The method according to the presentinvention does not necessarily require the multiple beams, but can beapplied to an evaluation of a pattern when a single beam is used forscanning.

[0296] The electron beam apparatus described with reference to FIGS. 48through 50 can ensure a required S/N ratio even at a higher scanningspeed, and also ensure a high S/N ratio even without an averagingprocess. Also, since the beam diameter or beam current can be selectedin accordance with a pattern under evaluation to maximize the S/N ratio,a high throughput can be realized at a high resolution irrespective ofthe size of a pattern under evaluation.

[0297]FIG. 51 illustrates a further embodiment of the electron beamapparatus according to the present invention. This electron beamapparatus employs the electro-optical system in the embodimentillustrated in FIG. 8, and adds a device for preventing excessiveirradiation of electron beams. Therefore, description on components andoperations identical to those of the electron beam apparatus in theembodiment of FIG. 8 is omitted, and operations related to the newlyadded components will be described.

[0298] In FIG. 51, 26-11 designates trajectories of two secondaryelectrons positioned on a diameter, out of secondary electrons emittedfrom points on a circumference irradiated with primary electron beams,which are emitted onto the surface of the wafer W in the verticaldirection. An iris 28-11 is provided at a position at which thesetrajectories intersect the optical axis such that the aberration becomessmaller than a minimum value of beam spacings or distances of theprimary electron beams, as converted on the surface of the wafer. Also,in FIG. 51, 730 designates an axially symmetric electrode for measuringa potential of a pattern on the wafer W.

[0299] How to control the amount of irradiated primary electron beamswill be described. Multiple beams are deflected by a deflector 35-11 atfly-back of scanning, the beams are blocked by a knife edge 37-11 forblanking, a current absorbed by the knife edge is measured by a currentmeter 39-11, and the amount of irradiation per unit area is calculatedby an irradiation amount calculating circuit 41-11. This value is storedin a storage device 45-11 through a CPU 43-11. The irradiation amountcalculating circuit 41-11, CPU 43-11, and storage device 45-11 areincluded in a control unit 2 (FIG. 1).

[0300] Further, when the resulting amount of irradiation per unit areaincreases to a predetermined value, for example, 2 μc/cm² or more, anelectron gun control power supply 47-11 is controlled by an instructionfrom the CPU 43-11 to reduce a voltage applied to a Wehnelt electrode721 b, thereby reducing a beam current and the amount of irradiation.Also, if the amount of irradiation per unit area exceeds, for example, 3μc/cm² due to a delay in control, irradiation amount data related to thepertinent irradiated region is only output from an output device 49-11,while the evaluation is continued. In this event, the entire surface ofthe wafer is displayed on a CRT, and a region irradiated with anexcessive amount of irradiation is colored, as illustrated in an upperregion of FIG. 52, to display for the operator. Further, when the amountof irradiation per unit area exceeds a larger value, for example, 5μc/cm², the evaluation is once stopped.

[0301]FIG. 52 is a diagram for explaining how to measure the amount ofirradiation to the wafer W. The wafer W is divided into a large numberof chips 53-11, each of which is divided into regions 55-11, called astripe, in parallel with a direction in which the stage is continuouslymoved (in the Y direction in the illustrated example). Image data isacquired as the stage is moved in stripe widths. An enlarged view of thestripe is shown in a lower region of FIG. 52. Within a stripe 55-11,nine multiple beams 56-11 formed in the primary optical system arearranged in the X direction, for example, at equal intervals of 100 μm.These beams are scanned in the X direction over a width of 102 μm (arange indicated by 58-11 in the figure). A width of 1 μm on each side of100 μm range is a scanned region which overlap with an adjacent beam oran adjacent stripe.

[0302] Viewed at a certain time during acquisition of image data, all ofthe nine multiple beams 56-11 fall under a region of 900 μm×900 μmsquare indicated by 57-11. This region is defined as a unit area. If abeam current per unit area becomes abnormally large during acquisitionof image data, the output device 49-11 outputs how many times the beamcurrent per unit area of 900 μm×900 μm indicated by 57-11 has increasedmore than a normal magnitude.

[0303] As described above, the beam current is measured by measuring acurrent absorbed by the knife edge 37-11 in fly-back of scanning. Thismeasurement involves repetitions of periodic image data acquisition andcurrent measurement in such a manner that, for example, after image datais acquired by scanning the beam for 10 μs, the current is measured for1 μs, and after image data is again acquired for 10 μs, the current ismeasured for 1 μs. Then, only when the measured current exceeds apredetermined value, this measurement is output as an abnormal current.For example, in FIG. 52, if the beam current exceeds a defined valueduring acquisition of image data for a solid black region of a chipindicated by 59-11, this region is colored for display on a monitor.

[0304] The defined value for the beam current can be determined based onexperiment data on the amount of irradiation and breakdown of a gateoxide film, and as a value multiplexed by a sufficiently safetycoefficient in an actual integrated circuit or TEG (Test Element Group).

[0305] Also, when the beam current per unit area begins to increase froma normal value which is set lower than the defined value, a voltageapplied to the Wehnelt electrode 721 b of the electron gun in FIG. 51 isincreased to reduce an electron gun current to reduce the beam current.

[0306] The electron beam apparatus according to this embodiment canadjust a focusing condition and an enlargement ratio of the secondaryoptical system independently of a lens condition in the primary opticalsystem. Also, since an upper limit is determined for the amount ofirradiation to a sample per unit area, the performance and reliabilityof the sample will not be affected. Furthermore, the beam current can beadjusted with a simple manipulation.

[0307]FIG. 53 illustrates another embodiment of the electron beamapparatus according to the present invention. This electron beamapparatus adds a device for applying a decelerating electric fieldbetween an objective lens and a wafer, and a device for preventing adischarge of the wafer to the electron beam apparatus illustrated inFIG. 8. Therefore, description on components and operations identical tothose of the electron beam apparatus in FIG. 8 is omitted, andoperations related to the newly added components will be described indetail.

[0308] It is generally known that a secondary electron detectionefficiency is increased by utilizing reduced chromatic and sphericalaberrations of primary electron beams by applying a deceleratingelectric field between an objective lens and a wafer, and acceleratingsecondary electrons. However, if the sample is a wafer containing vias,attention should be paid. Specifically, when a large deceleratingelectric field is applied between the objective lens and wafer, and apredetermined value or more of primary electron beams are passed, thiswill end up on a discharge occurring between a via and the objectivelens, possibly damaging device patterns formed on the wafer. There arewafers more susceptible and less susceptible to such a discharge, andthe respective wafers are different in the condition under which adischarge occurs (the value of decelerating electric field voltage, andthe amount of primary beam current).

[0309] In the electro-optical system 70 in the electron beam apparatusillustrated in FIG. 53, an objective lens 726 is implemented as anelectrostatic lens, and a positive high voltage is applied to either ofelectrodes of the lens. On the other hand, the wafer W is applied with anegative high voltage by a voltage source 20-12. In this manner, adecelerating electric field is formed between the objective lens 726 andwafer W.

[0310] When the wafer W is formed with vias, primary electron beamsincident into a via causes a large amount of secondary electrons to beemitted therefrom since the vias are made of a metal having a highatomic number such as tungsten. Also, there are sharp metal patterns ofsub-micron diameters located near vias, so that a larger electric fieldis locally generated by the decelerating electric field. For thesereasons, the wafer formed with vias is quite susceptible to a discharge.

[0311] However, a discharge does not immediately occur even if such acondition is fully established. First, a corona discharge occurs,wherein a residual gas locally illuminates in a region in which a largeelectric field exists, and a transient state called a spark dischargenext appears, followed by a transition to an ark discharge. In thepresent specifications, a period from the corona discharge to the outsetof the spark discharge is called “a discharge leader phenomenon”. It hasbeen found that an arc discharge can be avoided to prevent the waferfrom being broken by reducing the beam current to reduce the primaryelectron beams to a fixed amount or less, or reducing the deceleratingelectric field voltage between the objective lens 726 and wafer W, ortaking both of these actions at the time of this discharge leaderphenomenon.

[0312] Also, since wafers more susceptible to a discharge and wafersless susceptible to a discharge differ in the decelerating electricfield voltage and the amount of primary electron beams with which adischarge occurs, it is desirable to know limit values for preventing adischarge for each wafer without fixing these values at low levels.

[0313] The electron beam apparatus illustrated in FIG. 53 comprises aphoto-multiplier tube (PMT) 19-12 and a wafer current meter 21-12 as adetector for detecting a discharge between the wafer W and objectivelens 726 or the discharge leading phenomenon to generate a signal. ThePMT 19-12 can detect light emission due to a corona discharge and an arcdischarge, and the wafer current meter 21-12 can detect an abnormalcurrent at the outset of a corona discharge and an ark discharge.

[0314] When the PMT 19-12 detects light emission due to a coronadischarge or the wafer current meter 21-12 detects an abnormal currentat the time of the discharge leader phenomenon, the information is inputto a CPU 22-12 in a control unit 2 (FIG. 1). A voltage of deceleratingelectric field and a beam current value (corresponding to the amount ofprimary electron beams) of the electron gun 1 serve as basic data fordetermining the condition for preventing a discharge. The CPU 22-12, inresponse to the input indicative of the light emission or abnormalcurrent, or both, conducts a control, i.e., reduces the voltage 20-12 ofdecelerating electric field, or sends a feedback signal to an electrongun 721 to reduce the beam current to reduce the primary electron beamsto a fixed amount or less so as to prevent a discharge. The CPU 22-21may conduct both of these controls.

[0315] While both of the PMT 19-12 and wafer current meter 21-12 arepreferably used, one of them may be omitted.

[0316]FIG. 54 shows the arrangement of devices on a single wafer W.While a plurality of rectangular chips 31-12 are taken from the circularwafer W, fragmentary chips, which are less than complete chips, exist inperipheral regions, as indicated by reference numerals 32-12, 33-12.These fragmentary chip regions are also subjected to normal lithographyand a variety of processes in a manner similar to the region of thecomplete chips 31-12. On the other hand, since these fragmentary chipsare not used as products, these regions may be broken without anyproblem. Therefore, when the regions of these fragmentary chips 32-12,33-12 are used to not only detect the discharge leader phenomenon butalso detect a discharge phenomenon without fear for breakdown, morecorrect determination can be made as to the condition for preventing adischarge. In this event, the PMT 19-12 detects light emission due to anarc discharge, while the wafer current meter 21-12 detects an abnormalcurrent at the time of the arc discharge to send a signal to the CPU22-12. In this manner, the CPU 22-12 can correctly indicate a voltagevalue for the decelerating electric field and the beam current value(corresponding to the amount of primary electron beams) as limit valuesat which no discharge occurs.

[0317] Since the electron beam apparatus described with reference toFIGS. 53 and 54 can set the limit condition for preventing a dischargein accordance with the discharge characteristics of a sample, the samplecan be prevented from a failure.

[0318]FIG. 55 illustrates a further embodiment of the electron beamapparatus according to the present invention. In this embodiment, anenergy filter device is added to the electron beam apparatus illustratedin FIG. 43. Therefore, description on components and operationsidentical to those of the electron beam apparatus in FIG. 43 is omitted,and operations related to the newly added components will be describedin detail.

[0319] In the electro-optical system 70 in the electron beam apparatusillustrated in FIG. 55, electron beams emitted from four locations onthe surface of a wafer W irradiated with four primary electron beams aredrawn by a positive voltage applied to one electrode 17-8 which formspart of an objective lens 8-8. The wafer W is applied with a lowervoltage by an electrode 18-1, which is axially symmetrically disposed onthe near side of the electrode 17-8 from the wafer W, to filter thedrawn secondary electron beams. Specifically, it is determined whetherthe secondary electron beams pass the objective lens, or is returned tothe wafer W, depending on whether they can pass over a potential barrieron the axis created by the electrode 18-8 which acts as an energyfilter.

[0320] Out of the secondary electrons emitted from the surface of thewafer W, those emitted from a pattern having a low voltage pass thebarrier created by the electrode 188, whereas those emitted from apattern having a high voltage cannot pass the electrode 18-8. From thisdifference, it is possible to measure a potential of a pattern on thewafer irradiated with the primary electron beams.

[0321] Alternatively, instead of applying a charge by irradiation ofelectron beams, the wafer W may be applied with a predetermined voltageby a power supply 19-8 through a connector 20-8 to measure a voltage ora current of a circuit pattern on the wafer W, thereby determiningdisconnection and short-circuit of the circuit pattern. In this event,since a time for applying a charge can be saved, a high throughput canbe provided.

[0322] Since the electron beam apparatus illustrated in FIG. 55 canselect whether a potential is applied to a wiring pattern on a sample orwafer from a connector or from electron beams, an increased degree offreedom can be attained for measurements. Also, since the energy filter(i.e., the electrode 18-8) is an axially symmetric electrode and has alarge hole near the optical axis, distortion and aberration of blur willnot occur, which would otherwise be experienced when a mesh electrodewas used, when the primary electron beams are scanned.

[0323]FIG. 56 illustrates another embodiment of the electron beamapparatus according to the present invention. This embodiment providesan electrostatic deflector 21-14 between the two enlarging lenses 741,742 in the secondary optical system of the electron beam apparatusillustrated in FIG. 8, and permits an alignment in the enlarging lens742 by the electrostatic deflector 21-14.

[0324] In connection with the electron beam apparatus illustrated inFIG. 56, processing involved in a defect test of a wafer W will bedescribed. It goes without saying that the processing involved in thedefect test according to the present invention, described below, can beapplied to the electron beam apparatus which uses an electro-opticalsystem of an arbitrary embodiment according to the present invention.

[0325] First, before describing the processing involved in the defecttest according to the present invention, processing involved in aconventional defect test will be described. Conventionally, thefollowing method has been prevalent.

[0326] On a wafer formed with a large number of the same type of dies indesign, secondary electron images are compared between the dies. Forexample, if a secondary electron image of a die detected first is notsimilar to a secondary electron image of another die detected at thesecond time (i.e., a difference between the secondary electron images islarger than a reference value), the second die is determined to have adefect if an image of a different die detected at the third time isidentical or similar to the first image (i.e., a difference between thesecondary electron images is smaller than the reference value).

[0327] A similar method can be applied to a mask or a wafer which isformed with two or more type of chips. In this event, secondary electronimages are compared for the same corresponding locations on these chips.If a difference is found at the same location as a result of acomparison of one chip with the other, it can be determined that eitherone is defective. Also, it is possible to eventually determine whetherany chip is defective from a comparison with the same location on theremaining chip.

[0328] However, there are several objects under testing which cannot besupported by the conventional defect testing apparatus as follows:

[0329] (i) When a mask is to be tested, the mask cannot be tested fordefects unless two or more chips are formed on the same substrate. Onthe other hand, such two-take masks tend to be reduced in future.

[0330] (ii) When a test is desired for checking whether or not acorrection for a proximity effect was appropriate in a transfer from amask to a wafer, the detection of defects becomes difficult. This isbecause even if a corrective effect is inappropriate, similar distortionappears with good reproductivity between adjacent dies, and the presenceor absence of defects cannot be determined in a die-to-die relativecomparison.

[0331] (iii) When it is desired to remove the presence or absence of aproblem inherent to a transfer device from a mask to a wafer, forexample, connections of stripes overlapping at all times, and thepresence or absence of a certain problem on the reproductivity such as arotation error remaining in a boundary between main fields, it isdifficult to detect such defects. This is due to similar reasons tothose of the problem (ii).

[0332] In a defect testing station according to the present invention,as described below, a defect testing method and apparatus, capable ofconducting a defect test based on a relative comparison betweendifferent locations in a logically identical form, can detect defects inregions under testing in which the defect test is impossible ordifficult with such a relative comparison.

[0333] In FIG. 56, the image processing unit 763 generates a patternimage on the surface of a wafer W based on electric signals from thedetectors 761, as described above, and the generated pattern image issupplied to a defect detector 50-14. Functional blocks of the defectdetector 50-14 is illustrated in FIG. 57. As illustrated in FIG. 57, thedefect detector 50-14 includes a control circuit 51-14 forcontrolling/managing respective components to determine defects on thewafer W; a pattern image comparator circuit 52-14 for executing acomparison based on secondary electron pattern images; a pattern imagememory 53-14 for storing the secondary electron pattern images; apattern data memory 54-14 for storing pattern data which is logical dataof patterns formed on the wafer W; and a logical pattern image formingcircuit 55-14 for forming logical pattern images to be compared with anactual secondary electron pattern image.

[0334] The pattern image comparator circuit 52-14 has a first mode forcomparing secondary electron pattern images at the same locations (forexample, dies when a wafer is concerned) on the wafer W in design; and asecond mode for comparing an actual secondary electron pattern image ata particular location on the wafer W with a logical pattern imagecorresponding to that location. The pattern image comparator circuit52-14 outputs differential data 59-14 indicative of a difference betweentwo images which are compared to the control circuit 51-14. Since thecompared images are more similar as the value of the differential data59-14 is smaller, the control circuit 51-14 can determine matching orunmatching of the two images based on this differential data 59-14. Thesecondary electron pattern image used by the pattern image comparatorcircuit 52-14 may be one directly sent from the image processing unit14-14, or one stored in the pattern image memory 53-14. These patternimages can be arbitrarily switched in a preferred manner.

[0335] A display unit 57-14 is connected to the control circuit 51-14for displaying results of comparisons and determinations, and the like.The display unit 57-14 may be comprised of a CRT, a liquid crystaldisplay, or the like, and can display a defect pattern 58-14, secondaryelectron pattern images, the number of defective locations, and thelike.

[0336] The pattern data stored in the pattern data memory 54-14includes, for example, mask pattern information and the like which isprovided from an input unit 56-14 installed outside. This input unit56-14 can enter instructions of the operator to the defect tester 50-14,and be implemented by a computer which has installed therein softwarecapable of creating pattern data.

[0337] Next, the flow of processing involved in the defect detectionwill be described along a flow chart of FIG. 58. First, a secondaryelectron image pattern at a location under testing on a wafer W isacquired (step S300). Details on this step will be described later.Next, it is determined whether the wafer W is a wafer or a mask (stepS302). When it is a wafer, it is determined whether or not the locationunder testing is highly susceptible to distortion in pattern formationdue to distortion in a transfer optical system in a transfer from a maskto the wafer or due to charge-up when a pattern is formed (a firstfactor) (step S304). Such a location has been previously mapped in amemory of the control circuit 51-14, or acquired from information fromthe input unit 56-14.

[0338] If the location under testing is highly susceptible to distortionin pattern formation due to the first factor (affirmative determinationat step S304), the pattern image comparator circuit 52 compares thesecondary electron image pattern at the location under testing with alogical pattern corresponding to that location (second mode) (stepS310). After the comparison, differential data 59-14 between bothpatterns is output to the control circuit 51-14.

[0339] If the location under testing is not susceptible to distortion inpattern formation due to the first factor (negative determination atstep S304), the flow proceeds to the next determination step S306. Inthis step, it is determined whether the location under testing is highlysusceptible to distortion in pattern formation due to a proximity effector an incorrect correction for the proximity effect in a transfer fromthe mask to the wafer, or a defective stripe connection or a defectivefield connection (second factor) (step S306).

[0340] If the location under testing is highly susceptible to thedistortion in pattern formation due to the second factor (affirmativedetermination at step S306), the pattern image comparator circuit 52-14compares the secondary electron image pattern of the location undertesting with the logical pattern corresponding to that location (secondmode) in a similar manner (step S310).

[0341] If the location under testing is not susceptible to thedistortion in pattern formation due to any of the first and secondfactors (negative determination at step S306), the logically identicallocations are compared with each other (first mode) (step S312). Asdescribed above, this is a step for comparing the secondary electronimage pattern of the location under testing with a secondary electronimage pattern at a location, which is a location different from thelocation of interest, but is formed with a logically identical pattern,to output differential data between the two. With a wafer, a die-to-diecomparison is mainly performed in many cases.

[0342] On the other hand, if the wafer W is determined to be a mask atstep S302, it is determined whether or not this mask is a two-take maskon which two or more of the same type of chips are formed (step S308).With a two-take mask (affirmative determination at step S308), logicallyidentical locations are compared with each other over two or more ofidentically formed chips (step S312). If the mask is not a two-take mask(negative determination at step S308), it is compared with a logicalpattern image (step S310).

[0343] After the comparisons as described above, the control circuit51-14 determines the presence or absence of defects based on thecalculated differential data 59-14 (step S314). In a comparison with alogical pattern image, “not defective” is determined when the value ofthe differential data 59-14 falls within a predetermined thresholdvalue, and “defective” is determined when it exceeds the thresholdvalue.

[0344] A determination method for use with the comparison of logicallyidentical locations with each other proceeds as follows. For example,FIG. 59A shows an image 31-14 of a die detected at the first time and animage 32-14 of another die detected at the second time. If it isdetermined that the die image 31-14 is dissimilar to the die image 32-14(i.e., the differential data value exceeds the threshold value), and animage of a different die detected at the third time is identical orsimilar to the first image 31-14 (i.e., the differential data value isequal to or less than the threshold value), it is determined that thesecond die image 32-14 is defective. When using a more sophisticatedcomparison and matching algorithm, it is also possible to detect adefective portion 33-14 in the second die image 32-14.

[0345] When determining to be defective as a result of the defectdetermination (affirmative determination at step S316), information ondefects is displayed on the display unit 57-14 (step S318). For example,there may be the presence or absence of defects, the number of defects,information on defective locations (positions), and the like. Also, forexample, a defective pattern image such as the second die image 32-14 inFIG. 59A may be displayed. In this event, a defective portion may bemarked.

[0346] Next, it is determined whether or not the wafer W has been testedover the entire region under testing (step S320). When the test is notcompleted (negative determination at step S320), the flow returns tostep S300, from which similar processing is repeated for the remainingregion under testing. When the test is completed (affirmativedetermination at step S320), the defect test processing is terminated.

[0347] In the foregoing manner, for testing a wafer for defects in thisembodiment, a comparison is first performed on a die-to-die basis fortesting (step S312), and then the die is compared with a logical patternimage for a location at which no defect can be detected by such acomparison due to similar defects occurring in the dies (step S310).Since such defects appear in all dies in a distorted region of interestwith good reproductivity, it is sufficient to test only one die for thedefects in the distorted region at step S310. In the flow chart of FIG.58, such locations at which reproducible defects may be present aredetermined at steps S304 and 306.

[0348] Further, this embodiment can implement a defect detection for amask irrespective of whether or not it is a two-take mask.

[0349] Since the secondary electron acquisition process at step S300 inFIG. 58 is similar to the description made in connection with the firstembodiment in FIG. 8, description thereon is omitted.

[0350] The defect detector 50-14 can also conduct the following defecttest.

[0351]FIG. 59B shows an example of measuring a line width of a patternformed on a wafer. An actual pattern 34-14 on the wafer is scanned in adirection 35-14 to generate actual secondary electrons, the intensitysignal of which is indicated by 36-14. A width 38-14 of a portion inwhich this signal continuously exceeds a threshold level 37-14previously determined through calibration can be measured as the linewidth of the pattern 34-14. If the line width measured in this mannerdoes not fall under a predetermined range, it can be determined that thepattern is defective.

[0352] A line width measuring method in FIG. 59C can also be applied toa measurement of an alignment accuracy between respective layers when awafer W is formed of a plurality of layers. For example, a secondalignment pattern formed in the second layer lithography has beenpreviously formed near a first alignment pattern formed in the firstlayer lithography. The alignment accuracy between the two layers can bedetermined by measuring the spacing between the two patterns by applyingthe method in FIG. 59B, and comparing the measured value with a designvalue. Of course, this method can be applied as well to a wafer formedof three or more layers. In this event, the alignment accuracy can bemeasured with a minimum amount of scanning if the spacing between firstand second alignment patterns is chosen to be substantially equal to aspacing between adjacent beams of a plurality of primary electron beamsin the electro-optical system 70.

[0353]FIG. 59C shows an example of measuring a potential contrast of apattern formed on a wafer. In the electro-optical system 70 illustratedin FIG. 56, an axially symmetric electrode 730 is provided between theobjective lens 726 and wafer W, and is applied, for example, with apotential of −10V with respect to a potential of 0 V on the wafer. Anequi-potential surface at −2 V in this event has a shape as indicated by40-14 in FIG. 59(c). Assume herein that patterns 41-14 and 42-14 formedon the wafer are at potentials of −4 V and 0 V, respectively. In thisevent, secondary electrons emitted from the pattern 41-14 have an upwardspeed corresponding to the motion energy of 2 eV on the equi-potentialsurface 40-14 at −2V, so that they pass over this potential barrier40-14, exit the electrode 730 as indicated by a trajectory 43-14, andare detected by the detectors 761. On the other hand, secondaryelectrons emitted from the pattern 42-14 cannot pass over the potentialbarrier at −2 V, and are driven back to the surface of the wafer asindicated by a trajectory 44-14, so that they are not detected. As such,a detected image of the pattern 41-14 is bright, while a detected imageof the pattern 42-14 is dark. Consequently, a potential contrast can beacquired for the region under testing on the wafer W. The potential of apattern can be measured from a detected image if the brightness andpotential of the detected image have been previously calibrated. Then, adefective portion of the pattern can be detected by evaluating thispotential distribution.

[0354] In FIG. 56, a blanking deflector 17-14 is provided to deflectprimary electron beams to a knife edge shaped beam stopper (not shown)positioned near a cross-over P1 at a predetermined period torepetitively pass the beams only for a short time period and block thebeams for the remaining time period, thereby making it possible tocreate a bundle of beams having a short pulse width. When such beamshaving a short pulse width are used to measure a potential on a waferand the like, the operation of a device can be analyzed at a hightemporal resolution. In other words, this defect test can be used as aso-called EB tester.

[0355] As described above, since the defect test can alternately compareimages of different locations in a logically identical form on a sampleor compare a logical standard image with an actually generated image,the test can be conducted with a high accuracy and a high throughputirrespective of whether or not potential defects are reproducible. Also,since reproducible defects and non-reproducible defects can be testedwith the same apparatus, a foot print of a clean room can be reduced.

[0356] Referring to FIGS. 60 through 66, description will be made on theprocessing for preventing a degraded accuracy for the defect detectioneven when a misregistration occurs between an image of secondaryelectron beams acquired by scanning primary electron beams over a regionunder testing on the surface of a wafer and a previously providedreference image during the defect test processing. Such misregistrationconstitutes a particularly grave problem when a region irradiated withthe primary electron beams deviates from a wafer W to cause a portion ofa test pattern to be lost in a detected image of secondary electronbeams. This problem cannot be accommodated simply by optimizing amatching region within the detected image. Moreover, this is regarded asa critical disadvantage particularly in a test of highly definedpatterns.

[0357]FIG. 60 illustrates a defect detecting apparatus which employs themulti-beam based electro-optical system 70 in the electron beamapparatus illustrated in FIG. 8. This defect testing apparatus iscomprised of an electron gun 1-15 for emitting primary electron beams;an electrostatic lens 2-15 for deflecting and reshaping the emittedprimary electron beams; an ExB deflector 3-15 for directing the reshapedprimary electron beams through a field in which an electric field E isorthogonal to a magnetic field B and substantially perpendicular to awafer W; an objective lens 10-15 for focusing the primary electron beamson the wafer W; a stage apparatus 50 movable in a horizontal plane withthe wafer W carried thereon; an electrostatic lens 6-15 for enlargingsecondary electron beams emitted from the wafer W by the irradiation ofthe primary electron beams; detectors 7-15 for detecting an enlargeimage as a secondary electron image of the wafer W; and a controller16-15 for controlling the entire apparatus and for forming an image froma secondary electron signal detected by the detectors 7 to detectdefects on the wafer W based on the image. The controller 16-15 isincluded in a control unit 2 (FIG. 1). While images based on scatteredelectrons and reflected electrons, not limited to the secondaryelectrons, can be acquired as the electron image, described herein is asecondary electron image selected as the electron image.

[0358] An axially symmetric electrode 12-15 is additionally interposedbetween the objective lens 10-15 and wafer W. A control power supply isconnected to this axially symmetric electrode 12-15 for controlling afiltering effect of secondary electrons.

[0359] The detector 7-15 may be in an arbitrary configuration as long asit can convert secondary electron beams enlarged by the electrostaticlens 6-15 to a signal which can be subsequently processed.

[0360] As illustrated in FIG. 60, the controller 6-15 may be implementedby a general-purpose personal computer or the like. This computercomprises a controller body 14-15 for executing a variety of controlsand operational processing in accordance with a predetermined program; amonitor 15-15 for displaying results of processing performed by the body14-15; and an input unit 18-15 such as a keyboard, a mouse and the likefor the operator to enter instructions. Of course, the controller 16-15may be implemented by hardware dedicated to a defect testing apparatus,or a workstation or the like.

[0361] The controller body 14-15 is comprised of CPU, RAM, ROM, harddisk, a variety of control boards such as a video board, and the like,not shown. On a memory such as RAM or hard disk, a secondary electronimage storage region 8-15 is allocated for storing electric signalsreceived from the detectors 7-15, i.e., digital image data on asecondary electron image of the wafer W. Also, on the hard disk, areference image storage unit 13-15 exists for previously storingdefect-free reference image data on the wafer. The hard disk furtherstores a defect detection program 9-15, other than a control program forcontrolling the entire defect testing apparatus, for reading thesecondary electron image data from the storage region 8-15 toautomatically detect defects on the wafer W in accordance with apredetermined algorithm based on the image data. As described later ingreater detail, the defect detection program 9-15 has a function ofmatching a reference image read from the reference image storage unit13-15 with an actually detected secondary electron beam image toautomatically detect a defective portion, and display an alarm for theoperator when determining defective. In this event, the secondaryelectron image 17-15 may be displayed on the monitor 15-15 for warning.

[0362] In the defect test processing, as illustrated in the flow of amain routine in FIG. 61, a wafer W under testing is first set on thestage apparatus 50 (step S400). This may be performed, as previouslyillustrated in FIG. 1, by automatically setting a large number of wafersW stored in a loader one by one onto the stage apparatus 50.

[0363] Next, the defect testing apparatus acquires each of images of aplurality of regions under testing displaced from one another, whilepartially overlapping on an X-Y plane on the surface of the wafer W(step S404). As illustrated in FIG. 62, a plurality of regions undertesting to be acquired refer to rectangular regions indicated byreference numerals 32-15 a, 32-15 b, . . . , 32-15 k, . . . , forexample, on a surface 34-15 under testing of the wafer W, which, asappreciated, are displaced, while partially overlapping one another,around a test pattern 30-15 of the wafer. For example, as illustrated inFIG. 63, assume that 25 images 32-15 (images under testing) of regionsunder testing have been acquired. In the image illustrated in FIG. 63, asquare cell corresponds to one pixel (or a block unit larger than apixel), and solid black cells of them correspond to image portions ofpatterns on the wafer. Details on this step S404 will be described laterin connection to a flowchart of FIG. 64.

[0364] Next, image data on a plurality of regions under testing acquiredat step S404 is compared on a one-by-one basis with reference image datastored in the storage unit 13-15 (step S408 in FIG. 61) to determinewhether or not defects are present on the surface of the wafer W undertesting, which are included in the plurality of regions under testing.This step involves so-called matching between image data, details ofwhich will be described later in connection with a flow chart of FIG.65.

[0365] If it is determined from the result of comparison at step S408that defects are present on the surface of the wafer W under testing,which are included in the plurality of regions under testing(affirmative determination at step S412), the operator is warned of theexistence of the defects (step S418). As a warning method, for example,a message notifying the existence of the defects may be displayed on themonitor 15-15, and simultaneously, an enlarged image 17-15 of thepattern in which the defects exist may be displayed. Such a defectivewafer may be immediately removed from a wafer chamber for storage in adifferent storage location from defect-free wafers W (step S419).

[0366] If it is determined from the result of comparison at step S408that the wafer W is free of defects (negative determination at stepS412), it is determined whether or not a region to be tested stillremains on the wafer currently under testing (step S414). When a regionto be tested still remains (affirmative determination at step S414), thestage 50 is driven to move the wafer W such that another region to benext tested enters a primary electron beam irradiated region (stepS416). Then, the flow returns to step 404 to repeat similar processingfor the other region.

[0367] When no region to be tested remains (negative determination atstep S414), or after the defective wafer removing step (step S419), itis determined whether or not the wafer W currently under testing is thelast wafer, i.e., whether or not any untested wafer still remains in theloader (step S420). When it is not the last wafer (negativedetermination at step S420), the tested wafer is stored in apredetermined storage location, and a new untested wafer is set insteadon the stage apparatus 50 (step S422). Subsequently, the flow returns tostep S404 to repeat similar processing on the new wafer. When it is thelast wafer (affirmative determination at step S420), the tested wafer isstored in the predetermined storage location, followed by termination ofthe entire flow.

[0368] Next, the flow of processing at step S404 will be described alongthe flow chart of FIG. 64. In FIG. 64, an image number i is first set toan initial value “1” (step S430). This image number is an identificationnumber sequentially given to each of a plurality of images of regionsunder testing. Next, an image position (X_(i), Y_(i)) is determined forthe region under testing having the image number i set thereto (stepS432). This image position is defined as a particular position withinthe region for defining the region under testing, for example, thecenter position within the region. At the current time, since i=1, imageposition is (X₁, Y₁), which corresponds, for example, to the centerposition of a region 32 a under testing shown in FIG. 62. The imagepositions have been previously determined for all image regions undertesting, and stored, for example, on the hard disk of the controller16-15, and read at step S432.

[0369] Next, the controller 16-15 applies potentials to deflectingelectrodes 19-15 and 3-15 such that primary electron beams passingthrough a deflecting electrode 13-15 in FIG. 60 are irradiated to theimage region under testing at the image position (X_(i), Y_(i))determined at step S432 (step S434 in FIG. 64). Then, primary electronbeams, emitted from the electron gun 1-15, pass the electrostatic lens2-15, ExB deflector 3-15 and objective lens 10-15, and is irradiated tothe surface of the set wafer W (step S436). In this event, the primaryelectron beams are deflected by an electric field crated by thedeflecting electrodes 19-15 and 3-15 and irradiated over the entireimage region under testing at the image position (X_(i), Y_(i)) on thetested surface 34-15 (FIG. 62) of the wafer W. When the image numberi=1, the region under testing is indicated by 32 a-15.

[0370] Secondary electrons and/or reflected electrons (hereinafterreferred only to the “secondary electrons”) are emitted from the regionunder testing irradiated with the primary electron beams. Then, thegenerated secondary electron beams are focused on the detector 7-15 at apredetermined magnification by the electrostatic lens 6-15 in theenlarging projection system. The detector 7-15 detects the focusedsecondary electron beams, converts the secondary electron beams to anelectric signal, i.e., digital image data for each detected device, andoutputs the electric signal (step S438). Subsequently, the digital imagedata of the detected image number i is transferred to the secondaryelectron image storage region 8-15 (step S440).

[0371] Next, the image number i is incremented by one (step S442), andit is determined whether or not the incremented image number (i+1)exceeds a constant value i_(MAX) (step S444). This i_(MAX) indicates thenumber of images under testing to be acquired, and is “25” in theaforementioned example in FIG. 63.

[0372] When the image number i does not exceed the constant valuei_(MAX) (negative determination at step S444), the flow again returns tostep S332 to again determine an image position (X_(i+1), Y_(i+1)) forthe incremented image number (i+1). This image position is away from theimage position (X_(i), Y_(i)) determined in the preceding routine by apredetermined distance (ΔX_(i), ΔY_(i)) in the X direction and/or Ydirection. In the example of FIG. 62, the region under testing islocated at the position (X₂, Y₂) displaced from (X₁, Y₁) only in the Ydirection, and is a square region 32 b-15 indicated by a broken line.The value of (ΔX_(i), ΔY_(i)) (i=1, 2, . . . , i_(MAX)) can bedetermined as appropriate from data which empirically indicates how longa pattern 30-15 on the surface under testing 34-15 of the wafer Wdeviates from the field of view of the detector 7-15, and the number andarea of regions under testing.

[0373] Then, the processing at steps S432 - 442 is sequentially repeatedfor the regions under testing at i_(MAX) locations. As illustrated inFIG. 62, these regions under testing are shifted in position, whilepartially overlapping, on the surface under testing 34-15, such that animage position (X_(k), Y_(k)) after k times of movements reaches animage region 32 k-15 under testing. In this manner, 25 pieces of imagedata under testing, illustrated in FIG. 63, are fetched in the imagestorage region 8-15. It is understood that the plurality of acquiredimages 32-15 representing the regions under testing (images undertesting) partially or completely cover the image 30 a-15 of the pattern30-15 on the surface under testing 34-15 of the wafer W, as illustratedin FIG. 63.

[0374] When the incremented image number i exceeds i_(MAX) (affirmativedetermination at step S444), the flow returns from this subroutine tothe comparison step (step S408) in the main routine of FIG. 61.

[0375] The image data transferred to the memory at step S440 iscomprised of the intensity value (so-called solid data) of the secondaryelectrons for each pixel detected by the detector 7-15. The image datacan be stored in the storage region 8-15 after subjected to a variety ofoperational processing for matching with a reference image at a latercomparison step (step S408 in FIG. 61). Such operational processing mayinclude normalization for unifying the size and/or concentration ofimage data to the size and/or concentration of reference image data,processing for removing isolated pixel groups which include apredetermined number of pixels or less, regarded as noise, and the like.Further, rather than simple solid data, the image data may have beencompressed or converted to a feature matrix which comprises featuresextracted from a detected pattern to such an extent that the detectionaccuracy is not degraded for a high definition pattern. Such a featurematrix may be, for example, an mxn feature matrix which comprises aseach matrix element the total sum (or normalized value derived bydividing the total sum value by the total number of pixels in the entireregion under testing) of secondary electron intensity values of pixelsincluded in each of mxn blocks (m<M, n<N) divided from a two-dimensionalregion under testing comprised of MxN pixels. In this event, thereference image data is also stored in the same representation as that.The image data herein referred to in the embodiments of the presentinvention includes image data, the features of which are extracted by anarbitrary algorithm in this manner, not to mention simple solid data.

[0376] Next, the flow of processing at step S408 will be described alongthe flow chart of FIG. 65. First, the CPU of the controller 16-15 readsreference image data from the reference image storage unit 13-15 into aworking memory such as RAM (step S450). This reference image isindicated by reference numeral 36-15 in FIG. 63. Then, the image numberi is reset to “1” (step S452), and image data under testing having theimage number i is read from the storage region 8-15 into the workingmemory (step S454).

[0377] Next, the read reference image data is matched to the data on theimage i to calculate a distance value D_(i) between the two data (stepS456). This distance value D_(i) represents a similarity between thereference image and the image i under testing, and shows that adifference between the reference image and image under testing is largeras the distance value is larger. Any amount may be employed as thedistance value D_(i) as long as it represents the similarity. Forexample, when image data is comprised of MxN pixels, the secondaryelectron intensity (or feature amount) of each pixel is regarded as eachposition vector component of an MxN-dimensional space, and the Euclideandistance between a reference image vector and an image i vector on theMxN-th dimensional space, or a correlation coefficient may becalculated. Of course, a distance other than the Euclidean distance, forexample, a so-called urban land distance and the like may be calculated.Further, when the number of pixels is large, the amount of calculationsbecomes immense, so that the distance value between image datarepresented by an mxn feature vector may be calculated, as describedabove.

[0378] Next, it is determined whether or not the calculated distancevalue D_(i) is smaller than a predetermined threshold value Th (stepS458). This threshold value Th is experimentally found as the basis fordetermining sufficient matching between the reference image and imageunder testing. When the distance value D_(i) is smaller than thepredetermined threshold value Th (affirmative determination at stepS458), the surface under testing 34-15 of the wafer W is determined as“non defective” (step S460), followed by the subroutine returning to themain routine. Specifically, if any of images under testing substantiallymatches the reference image, the surface under testing is determined as“non defective.” Since all images under testing need not undergo thematching in this manner, fast determination is possible. In the exampleof FIG. 63, it can be seen that images under testing at the third row,third column do not shift in position from the reference image andsubstantially match the same.

[0379] When the distance value D_(i) is equal to or larger than thepredetermined threshold Th (negative determination at step S458), theimage number i is incremented by one (step S462), and it is determinedwhether or not the incremented image number (i+1) exceeds the constantvalue i_(MAX) (step S464).

[0380] When the image number i does not exceed the constant valuei_(MAX) (negative determination at step S464), the flow returns again tostep S354, where image data is read for the incremented image number(i+1), and similar processing is repeated. On the other hand, when theimage number i exceeds the constant value i_(MAX) (affirmativedetermination at step S464), the surface under testing 34-15 of thewafer W is determined as “defective” (step S466), followed by the flowreturning from this subroutine. Specifically, when none of the imagesunder testing substantially matches the reference image, the surfaceunder testing 34-15 of the wafer W is determined as “defective.”

[0381] While FIG. 60 shows an example in which the electro-opticalsystem of the first embodiment is used to conduct a defect test, it goeswithout saying that a mapping type electron beam apparatus in otherembodiments may be utilized, not limited to the scanning type firstembodiment. In this event, the image position (X_(i), Y_(i)) at stepS432 in FIG. 64 corresponds to the center position of a two-dimensionalimage which is a combination of a plurality of line images acquired byscanning multiple beams. This image position (X_(i), Y_(i)) issequentially changed in subsequent steps by changing an offset voltageof the deflector 727 (FIG. 8), by way of example. The deflector 727changes a voltage around a set offset voltage to perform normal linescanning. Of course, a deflection device different to from the deflector727 may be provided to change the image position (X_(i), Y_(i)).

[0382] As described above, since a plurality of images of regions undertesting mutually displaced while partially overlapping on a sample areacquired and compared with a reference image to detect defects, it ispossible to prevent a degraded test accuracy due to the positions of theimages under testing and the reference image.

[0383] As previously described in connection with FIG. 1, a wafer to betested is carried by an atmospheric conveyance system and a vacuumconveyance system, aligned on a high precision X-Y stage, and then fixedby an electrostatic chuck mechanism or the like, followed by a defecttest and the like in accordance with a procedure of FIG. 66. Asillustrated in FIG. 66, first, an optical microscope is used to confirmthe positions of respective dies and detect the heights of respectivelocations as required, to store data. The optical microscope is alsoused to acquire optical microscopic images of sites at which defects andthe like are preferably monitored for comparison with electron beamimages, and the like. Next, the apparatus is applied with information onprescriptions in accordance with the type of wafer (after which process,whether the size of the wafer is 20 cm or 30 cm, and the like).Subsequently, after specifying locations to be tested, setting theelectro-optical system, and setting testing conditions and the like, thewafer is tested for defects in real time while images are acquired. Ahigh-speed information processing system comprising algorithms conductsthe test through comparison of cells, comparison of dies and the like,and outputs the result of test to a CRT or the like, and stores theresult in a storage device, as required. Defects include particledefects, abnormal shape (pattern defect), electric defects (disconnectedwires, vias and the like, defective conduction, and the like), and thelike. The information processing system is capable of automaticallydistinguishing such defects from one another, classifying the defects bysize, and sorting out killer defects (grave defects which disable theuse of a chip, and the like) in real time. The detection of electricdefects can be achieved by detecting abnormal contrast. For example,irradiation of an electron beam (approximately 500 eV) to a defectivelyconducting location can result in distinction from normal locationsbecause such location is generally charged in positive to cause lowercontrast. An electron irradiating apparatus used herein refers typicallyto a low-potential energy electron beam irradiator (generation ofthermal electron, UV/photoelectron) provided separately from an electronbeam irradiating apparatus for testing in order to emphasize thecontrast by potential difference. Before irradiating a region undertesting with an electron beam for testing, this low-potential energyelectron beam is generated for irradiation. For an image projectionsystem which can positively charge an object under testing simply byirradiating the electron beam for testing, the low-potential electronbeam irradiator need not be provided in separation depending on aparticular use. Defects can also be detected from a difference incontrast (caused by a difference in the ease of flow in the forwarddirection and opposite direction of a device) by applying a wafer with apositive or negative potential with respect to a reference potential.This can be utilized in a line width measuring apparatus and an aligner.

[0384] As the electro-optical system 70 operates, floating targetsubstances are attracted to a high voltage region due to a mutualproximity effect (charging of particles near the surface), so thatorganic materials are deposited on a variety of electrodes used forforming and deflecting electron beams. Since insulating materialsgradually deposited on surfaces due to charging in this manner adverselyaffect the formation of electron beams and the deflecting mechanism, thedeposited insulating materials must be removed on a periodic basis. Theperiodic removal of insulating materials can be carried out by utilizingelectrodes near regions on which insulating materials are deposited tocreate a plasma of hydrogen, oxygen or fluorine, and a compoundincluding them, such as HF, O₂, H₂O, C_(M)F_(M) in vacuum, maintaining aplasma potential within the space at a potential at which sputter isgenerated on the surfaces of the electrodes (several kV, for example,20-50 kV), and removing only organic substances through oxidization,hydronization or fluorination.

[0385] Next, explanation will be made on a method of manufacturingsemiconductor devices which includes procedures for evaluating thesemiconductor wafers in the middle of a manufacturing process or afterthe process using the electron beam apparatus of the present invention.

[0386] As illustrated in FIG. 67, the method of manufacturingsemiconductor devices, when generally divided, comprises a wafermanufacturing step S501 for manufacturing wafers; a wafer processingstep S502 for processing wafers as required; a mask manufacturing stepS503 for manufacturing masks required for exposure; a chip assembly stepS504 for dicing chips formed on a wafer one by one and bringing eachchip into an operable state; and a chip testing step S505 for testingfinished chips. Each of the steps may include several sub-steps.

[0387] In the respective steps, a step which exerts a critical influenceto the manufacturing of semiconductor devices is the wafer processingstep S502. This is because designed circuit patterns are formed on awafer, and a multiplicity of chips which operate as a memory and MPU areformed in this step.

[0388] It is therefore important to evaluate a processed state of awafer executed in sub-steps of the wafer processing steps whichinfluences the manufacturing of semiconductor devices. Such sub-stepswill be described below.

[0389] First, a dielectric thin film serving as an insulating layer isformed, and a metal thin film is formed for forming wires andelectrodes. The thin films are formed by CVD, sputtering or the like.Next, the formed dielectric thin film and metal thin film, and a wafersubstrate are oxidized, and a mask or a reticle created in the maskmanufacturing step S503 is used to form a resist pattern in alithography step. Then, the substrate is processed in accordance withthe resist pattern by a dry etching technique or the like, followed byinjection of ions and impurities. Subsequently, a resist layer isstripped off, and the wafer is tested.

[0390] The wafer processing step as described is repeated the number oftimes equal to the number of required layers to form a wafer before itis separated into chips in the chip assembly step S504.

[0391]FIG. 68 is a flow chart illustrating the lithography step which isa sub-step of the wafer processing step in FIG. 67. As illustrated inFIG. 69, the lithography step includes a resist coating step S521, anexposure step S522, a development step S523, and an annealing step S524.

[0392] After a resist is coated on a wafer formed with circuit patternsusing CVD or sputtering in the resist coating step S521, the coatedresist is exposed in the exposure step S522. Then, in the developmentstep S523, the exposed resist is developed to create a resist pattern.In the annealing step S524, the developed resist pattern is annealed forstabilization. These steps S521 through S524 are repeated the number oftimes equal to the number of required layers.

[0393] In the process of manufacturing semiconductor devices, a test isconducted for defects and the like after the processing step whichrequires the test. However, the electron beam based defect testingapparatus is generally expensive and is low in throughput as comparedwith other processing apparatuses, so that the defect testing apparatusis preferably used after a critical step which is considered to mostrequire the test (for example, etching, deposition (including copperplating), CMP (chemical mechanical polishing), planarization, and thelike).

[0394] As described above, according to the present invention, sincesemiconductor devices are manufactured while they are tested for defectsand the like after termination of each step or sub-step, which requiresthe test, using a multi-beam based electron beam apparatus whichpresents a high throughput, the semiconductor devices themselves can bemanufactured at a high throughput. It is therefore possible to improvethe yield rate of products and prevent defective products from beingshipped.

What is claimed is:
 1. An electron beam apparatus for irradiating asample with primary electron beams, and detecting secondary electronbeams generated from a surface of the sample by the irradiation toevaluate the sample surface, comprising: an electron gun having acathode for emitting primary electron beams, said cathode including aplurality of emitters for emitting primary electron beams, said emittersbeing arranged and spaced apart from each other on a circle centered atan optical axis of a primary electro-optical system; said emitters beingarranged such that when they are projected onto a straight line parallelwith a direction in which the primary electron beams are scanned,resulting points on the straight line are spaced at equal intervals. 2.An electron beam apparatus according to claim 1, wherein each of saidemitters comprises a plurality of emitter chips, and is controlled toemit the primary electron beam from one of said emitter chips.
 3. Anelectron beam apparatus according to claim 1, further comprising an ExBseparator, and an objective lens for accelerating secondary electronsemitted from the sample surface, wherein said ExB separator separatessaid secondary electrons from the primary electro-optical system anddirected to a secondary electro-optical system.
 4. An electron beamapparatus according to claim 3, wherein said ExB separator comprises anelectrostatic deflector having six or more electrodes, and a troidal orsaddle-shaped deflector arranged outside said electrostatic deflector.5. An electron beam apparatus according to claim 1, wherein: saidcathode of said electron gun comprises a plurality of emitters formed onan end surface facing the primary electro-optical system; and saidelectron gun further comprises a control electrode having a plurality ofapertures.
 6. An electron beam apparatus according to claim 5, wherein:said plurality of emitters have bottoms formed in the same plane, andsaid apertures of said control electrode are formed on the same plane;and said electron gun further comprises a mechanism for performing oneof an alignment of relative inclination and spacing of said two planes,and a horizontal alignment of said emitters of said cathode to saidapertures of said control electrode.
 7. An electron beam apparatusaccording to claim 1, wherein each of said emitters is formed near abottom thereof in the shape of cone.
 8. An electron beam apparatusaccording to claim 1, wherein said cathode is made of a materialincluded in a group consisting of LaB₆, Ta, and Hf.
 9. An electron beamapparatus according to claim 1, wherein said cathode has said emitterswhich are formed by cutting a surface of single crystal tantalum havinga surface crystal orientation of <310>.
 10. An electron beam apparatusaccording to claim 1, wherein said cathode has said emitters which areformed by cutting a surface of single crystal hafnium having a surfacecrystal orientation of <100>.
 11. An electron beam apparatus accordingto claim 8 or 9, wherein each of said emitters has a plain surface leftat the bottom thereof, said plain surface having a diameter of 50 μm orless, or a width of 10 μm or less in a radial direction of a circlecentered at the optical axis and a width of 100 μm or less in adirection orthogonal to the radial direction.
 12. An electron beamapparatus according to claim 1, further comprising: a speed detector fordetecting a moving speed of a stage for carrying the sample thereon; anda deflection amount correcting device included at least one of theprimary and secondary electro-optical systems for correcting the amountof deflection for at least one of the primary electron beams and thesecondary electron beams in accordance with the moving speed of thestage from said speed detector.
 13. An electron beam apparatus accordingto claim 1, further comprising a device for arbitrarily setting energyof electron beams in a range of 0.5 eV or higher.
 14. An electron beamapparatus according to claim 1, further comprising: an objective lensfor accelerating low energy electrons emitted from the sample surface;an ExB separator for deflecting electrons passing through said objectivelens toward the secondary electro-optical system; and a plurality ofdetectors for detecting the intensity of electrons collected through thesecondary electro-optical system to convert the intensity to an electricsignal, a spacing between irradiation points of the adjacent primaryelectron beams is set larger than a sum of an extending diameter of backscattered electrons on the sample and an equivalent blur amount on thesample of the secondary electro-optical system.
 15. An electron beamapparatus according to claim 1, wherein the spacing between the adjacentprimary electron beams is adjusted by changing a magnification of anelectro-optical system from a generation unit of the primary electronbeams to the sample.
 16. An electron beam apparatus according to claim1, further comprising an objective lens, and an ExB separator positionedbetween said objective lens and the next lens positioned near saidelectron gun, wherein said primary electro-optical system and saidsecondary electro-optical system share a single lens.
 17. An electronbeam apparatus according to claim 1, further comprising a mechanism foradjusting a beam dimension or a beam current of the primary electronbeams to maximize a contrast or an S/N ratio in a particular pattern inelectric signals of the secondary electron beams detected by saiddetectors.
 18. An electron beam apparatus according to claim 17, whereinsaid particular pattern is a regular pattern having a pitch twice aminimum line width of a pattern on the sample under evaluation.
 19. Anelectron beam apparatus according to claim 1, further comprising: anirradiation amount detector for detecting the amount of primary electronbeams irradiated to the sample surface; and an irradiation amountcontroller for controlling to prevent the amount of irradiated primaryelectron beam per unit area from exceeding a previously setpredetermined value based on the amount of irradiation from saidirradiation amount detector.
 20. An electron beam apparatus according toclaim 19, wherein: said sample is a semiconductor wafer, said electronbeam apparatus further comprises a device for controlling to evaluate asurface of said semiconductor wafer in units of constant stripe widthswhile continuously moving said stage, and said irradiation amountcontroller is adapted to control every area smaller than the length in astripe direction of a chip multiplied by a stripe width.
 21. An electronbeam apparatus according to claim 1, wherein said sample is asemiconductor wafer, and said electron beam apparatus further comprises:an energy filter including an electrode for selectively passingtherethrough electrons exceeding particular energy of the secondaryelectrons emitted from wiring patterns on the semiconductor wafer todirect electrons having energy higher than the particular energy to thesecondary electro-optical system; and determining unit for comparing afluctuating state of electric signals from said detectors with afluctuating state of electric signals expected from a connectionrelationship of regular wiring patterns to determine defects of thewiring patterns, said defects including disconnection and short-circuit.22. An electron beam apparatus according to claim 21, further comprisinga device for switching a ground voltage and a predetermined voltage forapplication to a connector connected to an external electrode of thesemiconductor wafer.
 23. An electron beam apparatus according to claim21, wherein said energy filter comprises an axially symmetric electrode,and a power supply for applying said axially symmetric electrode with avoltage lower than a voltage on the semiconductor wafer.
 24. An electronbeam apparatus according to claim 1, further comprising: a dischargephenomenon detector for detecting a discharge between the sample and theobjective lens or a leading phenomenon thereof; and a condition settingunit for setting a condition for preventing a discharge based on anoutput from said discharge phenomenon detector.
 25. An electron beamapparatus according to claim 24, wherein said discharge phenomenondetector comprises a photo-multiplier tube (PMT) for detecting lightgenerated upon a discharge or a leading phenomenon, or a sample currentmeter for detecting an abnormal current generated in the sample upon adischarge or a leading phenomenon.
 26. An electron beam apparatusaccording to claim 24, wherein said condition setting unit is adapted toadjust a voltage of a decelerating electric field between the sample andthe objective lens or the amount of primary electron beams to prevent adischarge.
 27. An electron beam apparatus according to claim 24, whereinsaid discharge phenomenon detector is adapted to detect a discharge or aleading phenomenon thereof in a partial region of the sample which isnot used as a product.
 28. An electron beam apparatus according to claim1, further comprising: a plurality of detectors each for detecting theintensity of electrons collected through the secondary electro-opticalsystem to convert the intensity to an electric signal; and an imageprocessing unit for processing the electric signals from said detectorsinto image data.
 29. An electron beam apparatus according to claim 28,further comprising: a first comparator for comparing images, generatedby said image processing unit, of the same location of different chipson the sample; a second comparator for comparing an image of a standardpattern for the sample with an actual image of the sample generated bysaid image processing unit; a device for operating at least one of saidfirst comparator and said second comparator; and a device fordetermining defects on the sample based on at least one of results ofcomparisons performed by said first and second comparators.
 30. Anelectron beam apparatus according to claim 29, wherein said secondcomparator is adapted to compare an image of a particular location onthe sample which is expected to suffer defects when a pattern undertesting is formed on the sample with a corresponding standard patternimage, or with a pattern image for the sample which is expected tosuffer less defects.
 31. An electron beam apparatus according to claim29, wherein said second comparator is adapted to compare an image of aparticular location on the sample which is expected to suffer any of asituation of a proximity effect when a pattern under testing is formedon the sample, defective stripe connection or defective field connectionwith a corresponding standard pattern image.
 32. An electron beamapparatus according to claim 1, further comprising: an image acquisitiondevice for acquiring a plurality of images of regions under testingdisplaced while partially overlapping one another on the sample; astorage device for storing reference images; and a defect determiningdevice for determining a defect on the sample by comparing a pluralityof images of the region under testing acquired by said image acquisitiondevice with a reference image stored in said storage device.
 33. Anelectron beam apparatus according to claim 1, wherein said stageapparatus comprises: a non-contact supporting mechanism based on ahydrostatic bearing, and a vacuum sealing mechanism based ondifferential pumping; and a partition positioned between a location onthe sample surface irradiated with the primary electron beams and saidhydrostatic bearing support of said stage apparatus, for reducingconductance, wherein a pressure difference is produced between theelectron beam irradiated region and said hydrostatic bearing support.34. An electron beam apparatus according to claim 33, wherein saidpartition contains said differential pumping structure.
 35. An electronbeam apparatus according to claim 33, wherein said partition has a coldtrap function.
 36. An electron beam apparatus according to claim 33,wherein two of said partitions are provided in the vicinity of anelectron beam irradiated position and in the vicinity of saidhydrostatic bearing.
 37. An electron beam apparatus according to claim33, wherein said hydrostatic bearing of said stage apparatus is suppliedwith a gas of dry nitrogen or highly pure inert gas.
 38. An electronbeam apparatus according to claim 33, wherein at least surfaces of partsof said stage apparatus facing said hydrostatic bearing are subjected toa surface treatment for reducing an emitted gas.
 39. An electron beamapparatus according to claim 1, wherein: the sample is carried on astage apparatus which is accommodated in a housing and supported byhydrostatic bearings with respect to said housing in a non-contactmanner; said housing for accommodating said stage apparatus isevacuated; and said electron beam apparatus further comprises adifferential pumping mechanism provided around a portion of saidelectron beam apparatus for irradiating the sample surface with theprimary electron beams for evacuating the irradiated region on thesample surface.
 40. An electron beam apparatus according to claim 39,wherein a gas supplied to said hydrostatic bearings of said stageapparatus is dry nitrogen or highly pure inert gas, said dry nitrogen orsaid highly pure inert gas being exhausted from said housing foraccommodating said stage apparatus, pressurized, and again supplied tosaid hydrostatic bearing.
 41. An evaluation system for evaluating asample, comprising: an electron beam apparatus according to claim 1; aworking chamber for accommodating a stage apparatus and a primaryelectron beam irradiating unit of said electron beam apparatus, saidworking chamber being controllable in a vacuum atmosphere; a loader forsupplying a sample onto said stage apparatus within said workingchamber; a potential applying mechanism disposed within said workingchamber for applying the sample with a potential; and an alignmentcontroller for observing a surface of the sample to control alignmentfor positioning the sample with respect to an electro-optical system ofsaid electron beam apparatus, wherein said vacuum working chamber issupported through a vibration isolator for isolating vibrations from afloor.
 42. An evaluation system according to claim 42, wherein: saidloader comprises a first loading chamber and a second loading chamberwhich are atmospherically controllable independently of each other, afirst conveyer unit for conveying a sample between the inside and theoutside of said first loading chamber, and a second conveyer unitprovided for said second loading chamber for conveying a sample betweenthe inside of said first loading chamber to said stage apparatus, andsaid evaluation system further comprises an mini-environment spacepartitioned for supplying a sample to said loader.
 43. An evaluationsystem according to claim 41, further comprising a laser interferencemeasuring device for detecting coordinates of an object under testing onsaid stage apparatus, wherein said alignment controller determines thecoordinates of the object under testing making use of a pattern whichexists on the sample.
 44. An evaluation system according to claim 41,wherein positioning of the sample includes rough positioning performedin said mini-environment space, and positioning in X-Y directions andpositioning in a rotating direction performed on said stage apparatus.45. A method of manufacturing semiconductor devices, said method usingan electron beam apparatus according to claim 1 for evaluation such as adefect test for semiconductor devices in the middle of or aftertermination of a manufacturing process.
 46. A method of manufacturingsemiconductor devices, said method using an evaluation system accordingto claim 41 for evaluation such as a defect test for semiconductordevices in the middle of or after termination of a manufacturingprocess.
 47. A method of evaluating a sample, using an electron beamapparatus comprising a primary electro-optical system for irradiatingsaid sample with primary electron beams, a detecting system fordetecting an electron intensity to output an electric signal, and asecondary electro-optical system for directing secondary electron beamsgenerated from a surface of the sample by the irradiation of the primaryelectron beams thereto, wherein, a cathode of an electron gun of saidprimary electro-optical system includes a plurality of emitters foremitting primary electron beams, said emitters being arranged and spacedapart from each other on a circle centered at an optical axis of aprimary electro-optical system, and said emitters being arranged suchthat when said emitters are projected onto a straight line parallel witha direction in which the primary electron beams are scanned, resultingpoints on the straight line are spaced at equal intervals.
 48. A methodof evaluating a sample according to claim 47, wherein said emitters ofsaid cathode of said electron gun are formed on an end surface facingthe primary electro-optical system; and said electron gun furthercomprises a control electrode having a plurality of apertures.
 49. Amethod of evaluating a sample according to claim 47, further comprisingthe steps of: accelerating secondary electrons emitted from the samplesurface by an objective lens; and deflecting said secondary electrons tosaid secondary electro-optical system by an ExB separator whichcomprises an electrostatic deflector having six or more electrodes, anda troidal or saddle-shaped deflector arranged outside said electrostaticdeflector.
 50. A method of evaluating a sample according to claim 47,further comprising the steps of: detecting a moving speed of a stage forcarrying the sample thereon; and calibrating the amount of deflectionfor at least one of the primary electron beams and the secondaryelectron beams in accordance with the moving speed of the stage detectedat the speed detection step.
 51. A method of evaluating a sampleaccording to claim 47, further comprising the steps of: adjusting a beamdimension or a beam current of the primary electron beams to maximize acontrast or an S/N ratio in a particular pattern in electric signals ofthe secondary electron beams detected by said detectors.
 52. A method ofevaluating a sample according to claim 47, further comprising the stepsof: detecting the amount of primary electron beams irradiated to thesample surface; and controlling to prevent the amount of irradiatedprimary electron beam per unit area from exceeding a previously setpredetermined value based on the amount of irradiation, obtained thestep of detecting the irradiated amount.
 53. A method of evaluating asample according to claim 47, further comprising the steps of: detectinga discharge phenomenon between the sample and the objective lens or aleading phenomenon thereof; and setting a condition for preventing adischarge based on an output obtained at the step of detecting thedischarge phenomenon.
 54. A method of evaluating a sample according toclaim 47, further comprising the step of: comparing an image of astandard pattern for the sample with an actual image of the samplegenerated by said electron beam apparatus, wherein an image of aparticular location on the sample which is expected to suffer defectswhen a pattern under testing is formed on the sample with acorresponding standard pattern image, or with a pattern image for thesample which is expected to suffer less defects.
 55. A method ofevaluating a sample according to claim 47, further comprising the stepsof: acquiring a plurality of images of regions under testing displacedwhile partially overlapping one another on the sample; storing referenceimages; and determining a defect on the sample by comparing a pluralityof images of the region under testing obtained at the step of acquiringwith a reference image stored at the step of string.
 56. A method ofevaluating a sample according to claim 47, further comprising the stepsof: supporting a stage apparatus for carrying the sample by ahydrostatic bearing in a non-contact manner; evacuating said stageapparatus by a differential pumping mechanism; providing a partitionpositioned between a location on the sample surface irradiated with theprimary electron beams and said hydrostatic bearing support of saidstage apparatus, for reducing conductance, to produce a pressuredifference between the electron beam irradiated region and saidhydrostatic bearing support.
 57. A method of evaluating a sampleaccording to claim 47, further comprising the steps of: supporting astage apparatus for carrying the sample by a hydrostatic bearing, to ahousing, in a non-contact manner; evacuating said housing containingsaid stage apparatus; differential pumping an irradiation region on thesample on which the primary electron beams are radiated.